Horses work off of release of pressure. If he gets into your space, use whatever method you have selected to back him up, whether is be shake his lead line, tap it with a stick, whatever works for you. The key is to stop correcting him the second he complies. That's the only way he knows he did what you wanted. Also, be sure to let him make the mistake first. An example would be a horse who likes to walk off when you're standing there holding the reins because you want to adjust a stirrup or something. If he's standing still, do nothing. If he takes a step, back him up and take off the pressure to allow him to stand still again. Wait for him to repeat the mistake and correct him again. Always correct to the degree he screwed up. That eliminates the mistake of over or under-correction. For example, if he only took one step forward, send him back one step. If he took 7, send him back 7. You get the idea. Most horses want to please and gelding just want leadership, so he should get it quickly. Whatever issue you're working on, work on it long enough to where he gets it, but don't bore him to death with it. Know when to quit.
You just have to see your distance...you don't have to like it.