Best bet is to go WOT at least once every day
That way when it's close to being dead, you'll feel it slip (VERY noticeable jump in RPM's with no increase in MPH).
Once you feel it slip you have maybe 1-2 weeks of NO WOT VERY CAREFUL driving to fix it or end up stranded somewhere.
Seriously, from 1st major slip of mine I got about 3 weeks of "extra" driving to gather parts and plan for the repair.