Invisible fence fouled...

Peanut, my cat, learned to beat the invisible fence that I installed in
my yard. He was using it for about 2 years with no incident. Peanut
did not seem to care that he couldn't get out. Then I turned down the
"power" a bit, so he would have a slightly bigger area to enjoy.

Well, the new "power" setting worked fine for a few days. But then he
somehow learned to escape. I think he would just run through the shock
area... and once he got outside, he was fine.

The real problem is that I turned the power back up, but Peanut can
still escape. And I don't think training him on this system again will
help.

I am considering purchasing something like this:
http://store.yahoo.com/comfort1st/petinfenpiff.html

....which can not be escaped from. Do you think it will be difficult to
re-train him? I know very little (i.e. nothing) about cat behavior.
All I know is that I am honored that Peanut allows me to commune with
his graciousness. My master thanks you for your contribution. :-|