I installed my own for my two boxers, and it didn't take much time at all for my youngest(about a year) to figure it out, she no longer needs the collar at all. My older "non friendly to other dogs" boxer, is about 75lbs, and ran right through the fence with the "standard" collar that comes with the Petsafe kit. I bought the "stubborn" dog collar off of eBay, and it put her on her ass the first few times she tried to wonder through it. After that, she doesn't even go close to the boundries.
I left the flags in the ground for about 2 weeks, and trained them as the instruction CD states, and it was no problem. They won't even go out of the yard when childern or other dogs walk by within 2-3 feet of their line.
Also to note, my neighbor has a huge yellow lab, and also has the electric fence, and our dogs will chase each other up and down the yard and never cross the line, people look at them like they're retarded if they dont realize there is a fence in place.
I have quite a few people that are in our Boxer rescue that use this fence with great success, even with the fostered dogs learning quickly.