Neighbors dog help!

There is a wooden fence seperating our daughters property from her neighbors. Recently the owner of one of the next door houses moved back into his house w/ his dog. The dog immediately dug under the fence & into her back yard and plays w/ her black lab. They get along fab. However, this uninvited dog terrorizes her cat, eats up all food in site, dumps, and chews up any and everything.
She will talk to neighbor tomorrow, Sat. about letting dog over to play only on invited terms. But in the meantime we want to put up a barrier to keep this dog out. Suggestions? My dh was thinking short rebar every foot along the fence line. I say use scrap wood and dig a trench. I know there is a solution.