Try, in addition to the halter obstacle course, teaching your horse to yield his hindquarters and shoulders away from you. Clinton Anderson has a really thorough, step by step instructional system to teach these maneuvers. Just remember, keep your hand by the horse's head when you disengage his hindquarters, or he'll just follow you in a circle, continuing to invade your space. If you don't have a stick and string to reinforce your cues, don't buy Clinton's (way too expensive). I've seen the same tool at Rod's.com for under $20. If you need the rope halter, TSC has them with a short lead pretty reasonably priced, and lead rope components and bulk rope to build your own in custom lengths and materials are handy. My newest horse is a real sweetie, but that loviness means some space invasion on the ground. A few weeks of these and other CA groundwork exercises, and I rarely have a problem anymore.