just call him and tell him he still owes you money. tell him if he doesn't pay within the next month you will not mow for him anymore and he can find someone else. rule #1: always get paid for a cut first before you cut someone's yard again. this is what i live by. of course if you do businesses and such they will be billed monthly usually. as far as residentials they pay for one cut before i will even go back for the next cut. keep yourself from getting burned that way.