Cut it off.

Seriously.

When my hair gets long enough that it is driving me crazy, I chop it off.

Another (less drastic) option is to buy a Buff, and cut a hole in the appropriate spot. Buffs don't seem to unravel very fast, so you may not need to hem the hole. Pull the ponytail through the hole, use the buff like a balaclava.

or cut off the hair...