Go down to the dollar store and buy the hundred 'rounds' of ammo, er, marbles, in the net bags. Leaves no trace if you miss they will shatter on impact, uh, what slingshot....Also, cheap bags of either round lead fishing sinkers, ball bearings, etc will float your boat for years to come. I never tire of my fun, and can plinkin' can be a great way to spend an afternoon iin the Summer! rig a 2x4 so you can place the cans on them and then hang a old sheet behind it a few yards back to catch your ammo. Does'nt get cheaper than this for good old fashioned fun for all ages! Yes, head shots on varmits drop them like stones, hope yer dog is a retriever type 'cause going into the briars to retrieve the wee bastids ain't part of the fun...Also, always do like the squirrels and keep the Sun to your back when hunting them.