We have a couple of mixed breeds that are predominantly yellow lab.
When we first got them as puppies, we enclosed the back yard in a
low-cost wire fence that comes in 50-foot spools at Home Depot. This
worked fine, until recently. They're just about a year old now and
have discovered that jumping the fence is a trivial matter.

We don't have the financial means to have an expensive chain link
fence installed, so we're about to buy an invisible fence. I'm
thinking that I'd like to place the invisible fence wire just outside
the existing wire fence.

Over the past year, they've worn a pretty heavy groove into the area
just inside the fence. They typically like to run along this path.
I'd like for them to be able to keep using that path, but I'd like to
deter them from jumping the fence.

Has anyone else done anything like this? How would you train the dogs
to know about the penalty for jumping the fence?