considered one for my boys.  ruled it out for various reasons, but mainly because I felt it would be less effective with the two of 'em.  there was a fair amount of skepticism as well, I just couldn't see a little zap stopping them if they were chasing down some small, furry thing.  I just trusted a physical fence more, although at my next place I definately want to put in a taller fence, to eliminate the possibility of them jumping it.  my current fence, I'm sure they could jump if they wanted to.