Prong Collar sizes

Heidi is not a large GSD (a little less than 60 pounds), and her neck measures 20".  I got a medium for her with extra links, based on my trainer's recommendations.  He prefers the medium size over the large...which surprised me.  But, he said the large is a heavier duty that is pretty hard to get on and off the dog.  He told me to steer away from the kind with a snap because they can open unexpectedly or just the opposite, get stuck.  Also, he recommends the Herme pinch collar (which I don't believe you can get at a Petsmart or Petco type store). 

I also prefer medium and add links.  I think Kenya's is a 14".  I can't really get the large on and off.  You're not supposed to slide it over their head and my hands aren't strong enough to pinch those links.  I use a medium with a quick release.  Neither of my dogs are reactive and I really only use a prong when training very specific things, so I don't need it to not fail, if that make sense.  I see way too many that aren't fitted correctly and the chain hangs off the dog's neck.  I'm not sure the placement of the collar on the neck is as important as some make it out to be, but fitting it correctly is important.  Whatever brand you get, make sure the prongs are rounded and smooth (Herm Sprenger, Top Paw).

  I will be ordering from PetEdge, and have already planned on ordering nothing but Herm Sprenger Prongs. There are absolutely NO petcos or petsmarts within an hour driving distance, so I have no choice but to order online or through magazines.

I always tell people that, when in doubt, go smaller.  For your dogs I'd probably suggest a medium for the Golden and possibly a large for the Rottie (though I'd try a medium first, I think).  You can always add links if they're not long enough. 

 Also, just a tip, I'd order a slip collar for the dogs to wear when they are wearing the prongs.  That way, if the prong does unexpectedly pop off, you still have your dog on leash.  They have some small parachute slip collars you can order off of petedge.com when you order your prongs.  They're very strong for their size, so don't think anything of how thin they are. 

Workingdoglover

I always tell people that, when in doubt, go smaller.  For your dogs I'd probably suggest a medium for the Golden and possibly a large for the Rottie (though I'd try a medium first, I think).  You can always add links if they're not long enough. 

 Also, just a tip, I'd order a slip collar for the dogs to wear when they are wearing the prongs.  That way, if the prong does unexpectedly pop off, you still have your dog on leash.  They have some small parachute slip collars you can order off of petedge.com when you order your prongs.  They're very strong for their size, so don't think anything of how thin they are. 

 Because the dog in question will be handled by a child, we've decided to go with the stronger prong(the 3 MM 18";). I thought that I'd have to order without a measurement, but I finally did get the chance to measure the dog's neck and it is about 20-21", so I'm also ordering 6 extra links.

I was definitely skeptical at first about using the prong because of the stories of prongs breaking and dogs getting loose. No dog will be allowed to wear only a prong, but must have it attached to another collar, whether that be a buckle, or choke(nylon or chain). *(Same with head collars, must have an additional collar attachment.) The dog already has a choke that fits, so we'll go the cheaper route and just use the choke as a second collar, rather than ordering the nylon choke. (I show in conformation as well, so I understand that the nylon is actually quite strong. :) )
 

 On the PetEdge website the Herms come in "Snap On" as well.. if the regular prong does not snap on, how do you get it on? You don't place them over the head!?

Just remember that the smaller the prongs, the bigger the correction (since there are more "prongs" to pinch...).  So bigger doesn't always mean better.  I actually have two for my dog.  The small I use for obedience work and perfecting heeling and such, and the medium I use in protection work, so he still gets a correction, but not big enough to make him not want to work anymore. 

 And as far as the snap-on question...

This is a snap-on... http://www.petedge.com/assets/product_images/styles/large/CP535_600X600.JPG
This is a regular...http://www.petedge.com/assets/product_images/styles/large/WH534_600X600.JPG

I much prefer the regulars.  To get them on and off, you just pinch one of the prongs together and it will sort of "unlock" and slide out of the other prong.  That's probably really confusing...it's super easy, though.  You should find someone that has used a prong correctly before and have them show you how to put it on and off and use it correctly.  Definitely NEVER slide a prong over a dog's head. 

 What is the difference between the snap and the regular? I knew that the links were supposed to just snap together and to never put it over the head. That was why I was so confused. If it couldn't fit or snap together, how could you put it on? But truly BOTH are snap on, so what is the difference? I understand that you must press the links together and then snap them on and off.

Mine has a quick release, so I don't put it on using the links.  There's a clasp in the martingale section of chain.  I just give it a pinch and the collar falls off.

 I have never used or suggested a large for anyone's dog, no matter how big the dog is. The large prongs IME are clunky, tend not to fit as well and arenot as effective. You would be best going with the medium for both dogs IMO.

I'd suggest a small/fine prong  for a big, powerful dog being handled by a child. The sizing is more than misleading- the collar acts by pinching the skin between the links, therefore the more links the more control the collar gives you. Like bits for horses- a big fat snaffle gives you a lot less "control" than a thin one.