My mare's mane does the same thing, if I don't have it braided 24/7 it gets knotted instantly. What do you have against braiding it? I find braids to be quite low maintenance, just make them loose and you only need to re-braid once a month or so.
Got to admit tho, the other poster with the masking tape, that don't sound to bad. Prob wont hold up well come winter tho, or lot of rain.