I have no experience with what I'm suggesting, so take it FWIW.
How about setting up one of those inflatable man things, have the blower on a timer set to run several times per day, and include a stereo device, or something similar, that would broadcast the sounds of gunshots or other noises at the same time that the blowup monster was running? By not running the device all the time, it could retain some of its surprise value.
