Walkie-Talkies, zip tie and duct tape.
Zip tie the transmit button down on one W-T. Duct tape it to the back of the target. Turn it on.
Take the other W-T back to the firing line, turn it on.
Shoot at the target. When you hit it, the 'gong' sound will be transmitted from the W-T on the target to the W-T with you.