You've never heard the old saying?..."A good dog never ****s in his own yard."

My house lab responded well to positive training. You might try that vs. shock collar or electric fence. We'd take her out to a spot, tell her to " do her bidness", when she'd go, we'd give her a small doggie treat. After 2-3 times, twice a day, she had it down. she'd go on command. Today, almost 9 years later, same thing. If she can't go, she wimpers and heads to the door or heel, knowing she ain't getting a treat. Just gotta be consistent.

You didn't train him to do that?

Supposedly Females are better about that.
My inside lab, i can let her out the front door, she'll walk down, do her business and come right back...(during the summer when she gets a wild hair,she decides she'll go swim in the bayou):pissed: but overall she's good about not going anywhere else