You do have to be careful about buzzing them as someone was prosecuted for doing this at Nayland some time ago.
Simplest thing is to set up for a landing, discover the runway is blocked and carry out a go-around...............
Concentrates the interlopers' minds a treat.
If I see the strip occupied, I shove the prop to fully fine at 501ft in the overhead, wait a few seconds till all eyes are skyward due to the change in engine noise, then I lower the gear.
It's worked on the one occasion I've done it: by the time the circuit to land was completed the strip was deserted.
Cusco
