Stop crank bolts loosening

If you're using the handy tool type allen key, you're probably are not levering enough torque on the bolt. I don't like the blue loctitie either. 14 have some excellent anit shake stuff that sorted my lock ring that was continuously coming loose when using the blue shite. If you are worried about over tightening refer to the manufacture's quoted values. If you need, I have a dial measuring torque wrench that you could use.
The best way to get a good fit is this:

1. Put the cranks on
   
2. tighten to the stated torque
   
3. take an easy ride for about 100 yards
   
4. then re-tighten to the stated torque
   
5. repeat parts 3 & 4 but increasing the intensity of each subsequent ride until the bolt/crank on longer moves up the taper.