You might consider placing liens on any real property
( house, car, bussines, Etc. ) it will cost you little or
nothing to file and he will have to settle with you when
he wants to sell any major asset or hire a lawer to
vacate the lien which will cost him money either way.
In addition liens can show up on credit reports and
be a big problem for him if he ever needs credit.

Best Regards
Tom.