The best way to catch a horse that doesn't want to be caught is to keep going into the field and NOT attempting to catch it! That way he/she won't learn that you only want them when you want them! Don't use titbits as that encourages demands you won't want. Just go and have a chat and let them know you aren't after anything, make friends and then clip on a lead rope and lead a biti and then release them again. Takes time but worth it...would you want to be caught if you knew there was work afoot? try and let me know. I will come up with some ideas if it doesn't! Good luck!