I have used things like water-filled balloons tied on strings, all connected by one long cord, so a pull on the long cord would get them all moving. If the strings are different lengths or the ballonon are filled with different amounts of water, they move at different rates. I was able to teach a girl who was a friend of my daughters to hit moving targets in one session. She is now a police cadet and scores quite well on the range. We have also used blown up balloons placed in a basket on a windy day, then tipped over. This is an especially good activity if there is snow on the ground, as you can see where your bullet is hitting, and the balloons bounce, so you really have to concentrate.