How to keep cats from climbing fence?

There are actually several systems sold to convert existing fencing into something your cats can't climb over (mind you, I still think I'd monitor) and if you Google cat fence or cat proof fence, you'll find them.  This is the system I saw that seemed pretty fool proof to me.
 
[linkhttp://www.purrfectfence.com/]http://www.purrfectfence.com/[/link]
 
I'm thinking of a small, full enclosure for mine someday...

What about having netting put over your yard.  It connects to the top of the fence and to your house.  Pofi_pasquale  That is an awesome invention!  I like that!  I keep my cats inside  but I may look into getting one of those so I can let them out!

If they are already indoor cats, I'd leave them indoors and maybe harness train them so they can go out with your supervision once in a while.  Outdoor or indoor/outdoor cats require additional vaccinations that also carry risks of cancer and complications from the vaccinations.  For example, I have indoor cats that are all negative for feline leukemia.  I don't vaccinate them, because they can only get this from an outdoor cat.  For an indoor cat, there is a greater chance of developing a tumor/cancer from the vaccine than somehow getting the disease.  Outdoor cats would need the vaccination, which is an added expense and added risk of complications.  Outdoor cats also need flea and tick prevention and can easily get worms or another parasite from eating junk outside.  I had my cat out once and he got stung by a bee, which was really bad for such a small animal.  We took one of our rabbits out and then found mites all in its fur.  IMO, the additional risks are just not worth the novelty, especially if the cats are already content indoors.

I posted this reply just recently to another poster.  I'm serious.  Get a low voltage solar powered horse fence cable and run it along the top of the fence.  No plug  ins to worry about and it still works in the coldest winter.
I'm telling you the first time the kitties get zapped they will NEVER try to climb the fence again.
I have 13 cats who have full access to my backyard which has 6 foot chain link.  Everyone has gotten zapped or witnessed a zapping and now my kitties are safe and so are the bunnies that visit my yard.

Hi, thanks for all of your replies. I've been so busy moving I kept forgetting to get on here. I would almost like the netting idea but that would look hideous and there's no way my roomate would agree to it.
 
I checked out that website, that arch at the top of the fence is actually what my mom suggested. I could just buy chicken wire and make kind of an upside-down U shape with it so that the cat hits a wire "ceiling" when they climb the fence.
 
nynative, what voltage is okay for the cats? I already have a solar powered hotwire fence from when I used to have horses. I'd have to go to my parents house to dig it out and check the voltage. Is there a way to lower the voltage?
 
And I probably wouldn't even let them out except when I was at least home, or outside with them. It's just that doing this will more than double their play area and I really think it's be a good thing for their sanity.
 
As for diseases, etc, well the yard will have a privacy fence so no other animals (other than the possible raccoon, etc maybe) will come into the yard. Flea control is no problem, I dust everything with diatomaceous earth. As for other cats coming into the yard, I doubt there will be THAT many loose cats in the area since we are near a mildly busy road; also I have dogs to deter cats from coming in as well as the hotwire fencing would probably keep animals out as well as in. The problem is that they AREN'T content indoors. My dog is a jerk to them, and the two cats don't really like each other. I already had to rehome one of my cats (to my best friend) due to daily fighting. I tried to rehome one of the cats I still have now but everytime someone would call about the ad, I'd be too scared to call them back, not knowing where she'd end up.
 
Again, thanks everyone for your replies!

I think the U at the top is the best idea.  I've never heard of electric fences made for safe use with cats.  Also, just like dogs (maybe even moreso) when a cat gets spooked, they run like they're shot out of a canon!  Once I scared my cat and he was running so fast that when he realize the door was shut, he had no choice to actually run all the way up the wall to the ceiling and did some kind of flip back down.  It was too funny.

If they're going out while you're supervising, you may not even need something at the top of the fence.  If they start climbing, give them a squirt of water and pretty soon they'll catch on.  You'll still be at risk for other disease spread through flies and such that go from animal to animal and bite, but if they're only going out when supervised they probably won't be out enough to get exposed to much.  As for the dog and cats getting along, I personally don't think just letting the cats outside for more room will solve any of the problems.  It may, but in my experience this usually makes it worse.  Dogs are so contextual that often they will ignore or put up with cats in the house, but outside their prey drive kicks in.  Putting them outside makes them prey in the eyes of the dog, and just gives them more territory to fight over amongst themselves (the cats).  I would work on these issues indoors before giving them even more space without being able to control how they treat each other.

Well the dog is only a jerk to them when they come near her. She doesn't want them in her space. Sometimes she gets mad when they play and she tries to break it up. Other than that, she leaves them alone. I just feel like if they weren't around her all the time she wouldn't be such a bully. I do need to invest in more squirt bottles now that you mention it.

I have one cat that loves to be outside.  I only let him out when I'm home and I keep him on a harness now.  He's not good with strangers so after having to retrieve him from my neighbors yard a couple times while he was screaming like im killing him, I had to start harnessing him. 
He doesn't care as long as he can be outside. 

For anyone needing to build a cat proof fence in the future the feral cat society has put out instructions on a much cheaper DIY version of the expensive mesh kits.  [linkhttp://www.feralcat.com/fence.html]http://www.feralcat.com/fence.html[/link]  I plan to set one up once I get a chain link fence in as a base to keep the dog in.
 
I don't think any of the electric fence ideas are good.  Cats are far more flighty than even horses.  I don't use electric wire with my horses but a much more visible 4" electric tape because if they panic and don't realize where the shock is coming from they are more likely to go forward through the fence instead of away from it.  A cat has an even greater chance of doing something like that and may just continue to leap over or duck under the wire.  Then you have a loose panicky cat that you may not be able to catch before it gets lost or injured.  Even if the cat does turn back they could injure themselves in their mad dash to get away.  Cats just get too stressed for something like that.  It would probably take me several days to a week to calm Carmel back down after even the mildest of electric fences and she'd refuse to go outside during that time.

Sham, that was the main reason I was doubting it. I didn't know if she'd actually be smart enough to know what was shocking her, and to turn around. For all I knew, she'd keep going over it. And what I have actually is the tape, it's bright yellow and black. What is funny is the cats actually don't seem to want to go outside, so I guess I'll just keep things as they are...