Also rat traps with de blade solderd to the swing arm work to
Neighbors' kids did something similar with gum rubber tubing tied between patio cover posts - launched bags of dog poo over the neighbors' roof & into the park beyond where a softball game was in progress. Hit the cop car, too when it arrived to investigate.Best way involves surgical tubing and a spaghetti strainer ...
Can't find the hi-res, but this has over 3 million views.
AA