Hi,
I've used a soda can with coins and duct tape to secure the top. It's worked on quite a few young geldings with the same behavior. I've never tried it with a mare and probably wouldn't. You can just shake the can or throw it at them - it's harmless, but can be effective. The biggest draw back is it may upset the other horses. The can has to be fucused on the culprit. It does take a few day for him to learn to settle down and the others to learn that they're not the target. He'll need voice repremand and the other need some follow up if they were startled.
I've used a soda can with coins and duct tape to secure the top. It's worked on quite a few young geldings with the same behavior. I've never tried it with a mare and probably wouldn't. You can just shake the can or throw it at them - it's harmless, but can be effective. The biggest draw back is it may upset the other horses. The can has to be fucused on the culprit. It does take a few day for him to learn to settle down and the others to learn that they're not the target. He'll need voice repremand and the other need some follow up if they were startled.