[Flat4boxer]

The best indicator of future behavior is past behavior. When he gets out, he will be back in your MILs yard and at some point will assault someone again.

If your MIL is like mine, a bit older and somewhat feeble, whatever less than lethal device she has may be taken from her and used against her.

There have been alot of good suggestions thus far and I think a good sized "sic balls" type dog is probably your best bet at this point.

Beyond that she will need a gun, the proper training on how to use it and the mental attitude to use it with deadly intention should it come to that. If she cannot bring herself to do that a gun is not an option at all because as I stated above, it may be taken from her and used against her.

I hate that you even have to come to others seeking this advise but it is the world we live in. Always remember, when seconds count, the police are minutes away.