When the fence was installed, was the perimeter flagged? We've never used an electronic fence, but I do know that flags are usually used to give the dog a visual idea of the area he's allowed in. If he doesn't have that cue, then for all he knows, there is no safe area.
"We are--each of us--dying; it's how we live in the meantime that makes the difference."
"It's not what you gather, but what you scatter that tells what kind of life you have lived!"
"Be kinder than necessary, for everyone you meet is fighting some kind of battle."