Had the same problem myself... whatever they use to fix the clamp to each section of pole is crap. This is what i do...
Use a stanley knife to mark the bottom of the clamp on the pole. Using araldite, paste it half way between the top of the pole and where the marker is (not too thick) then put the clamp back into place. Use some kitchen roll to wipe off and excess araldite off the pole.
Leave it over night and by the morning it will have set ready for the days work ahead. You wont have any problems with it slipping after that