I understand why you're so upset and rightly so. Since they are friends of the family and it sounds like he didn't do it maliciously but was trying to be funny (yes, I know, not so funny
) maybe just explain to him and his wife why it upset you so much and the fact that now you have to worry about your baby trying to dig under the fence and that he's to never do that again. Hopefully he'll understand and maybe learn to think before he does something like that again. I'm sure when his wife see's how upset you are she'll be sure to "keep him in line" in the future. If the friendship is important to you and he's sorry for what he did, you'll be able to forgive him and get past it. Good luck!