Water balloons, airsoft guns, air horns, water guns, rotten fruit, etc.
I would do any of that. Also, tie copper wires to your doorknob and the doorbell circuitry and ram the uninsulated ends into the wall socket. Shocking, I know.
You could also tie a Rottweiler to your front porch (unless you don't have one, of course)
Or you could tie some dental floss so that if they trip on it, a basket-full of scorpions or snakes fall on them.
I mean, the possibilities are endless really.
(But if you do something illegal, tell the police you don't know me)