I just had a scare...

Good for you and Teddi.  You would probably have to revive me after that.

Does the dog have an invisible fence? 

Nope, cause he didn't have a collar on, and once I seen him walking home from across the street.  

 He might have had one in the past, alot of owners get lax about the collar after the dog has gotten used to it or the dog only challenges the boundaries once in a while and gets away.  I absolutely HATE those things for just that reason.  I think invisible fences have taken several years off my life.  You're walking along, with your dogs on lead, you hear a snarl and scraping nails as the dog comes flying at you with teeth bared, no fence and no owner in sight and then it stops dead, right at the edge of the yard.  Geez Louise!!!  I also worry about those dogs when they're left out unattended because roaming dogs can get to them easily and there's nowhere for the invisible fenced dog to go. 

I just hate that the owners weren't out there with the dog, I know DH wanted to get an invisible fence for our backyard because its cheaper than fencing it in, but I vetoed it. I said not only will he let them out unattended (because he does that with our fenced yard, many times I pull down the driveway and the dogs are out unattended which I hate), Maggie would probably chase a bird or rabbit through the woods behind us regardless, her prey drive is ridiculous. 

Yeah, it's pretty amazing what dogs can tolerate if they're determined to do something.  My best friend had a GSD that was under threat of being confiscated by AC for excessive barking and lots of complaints from the neighbors.  In desperation she used a bark collar.  She came home from work and he'd burned a hole in his neck!  I would imagine an invisible fence is only going to shock for a few feet in front and in back of the boundary and a pretty driven dog would tolerate a few seconds of shock given the right motivation and high drive. 

years ago, when I was walking our mal/shepherd mix, a Bermese Mtn. dog came tearing down its front lawn snapping/snarling all the way. I thought I was gonna be shaking a dog off my leg.

My Daisy dog was very anti-dog, very strong and very silent. Her prey drive was pretty bad. She didn't even bark at this running dog. She stopped, looked it in the eye and that dog hightailed it home. Daisy sent that dog some kind of message that he got quickly.

Scary though - hard to get those jello legs moving again

 Yep, one bad thing about living in the ranches of South Florida is all the people who decide a big dog is the perfect lawn ornament for their large lawn.  I think the biggest scare I had was when four large dogs decided to pop the handle on their fence open and charge me and Kirby.  The only thing I think that saved Kirby was the fact my dad was there and managed at the last second with a loud yell and foot stomp get them to stop and turn tail back into their yard.  The other really scary moment was when a German Shepard charged Kirby and me.  There was no warning and I just barely caught his form out of the corner of my eye as he charged snarling from some bushes in his yard.  He had waited till we were nearly past so he could come at us from a backwards angle.  Thankfully he stopped abruptly at his property line.  It wasn't fear of an invisible fence though because as soon as we finished passing the remaining corner of his yard he nonchalantly stepped out in the street to sniff everywhere we had stepped.