Unless this is impossible to make, due to the fact horses are entities, I'm all for it. ^.^ I'm sure if it's possible, they're already working on a locking system.
+1 even though I haven't been on ECC while 1.6 has been out but this would help stop alot of problems.
Andrewkm I can try writing this and putting this on bukkit Ill said you the link when im done. Yes or no? Also I would need to know exactly what the person likes. So the horse can't leave a radius of 5 blocks or something.
I don't know if I'm going to sound really dumb... but does decompiling the jar file give you the source code? http://java.decompiler.free.fr/