What time does he leave for work? Post up in front of his house each morning for a week with your truck and trailer so all the neighbors realize he isn't paying you. He!!, I'd ask every neighbor that lives within sight of his yard "what time he/she leaves/gets home from work every day"? Just make sure you let them know that you are the landscaper and you can't get a hold of them.
There is an Old Blue Chair for each and every one of us, we just have to find it.
2006 GMC Sierra 2500hd crew cab
BOSS 8'2" Power V
Hustler X-one 60"
Toro Proline 36" wb w/t-bar controls
JS46 22" walk-behind (wouldn't recommend)
Shindaiwa T254, Echo trimmers, chainsaws, pole hedge trimmer, pole saw, hedge trimmer
Shindaiwa 633 and Husqvarna 130BT blower