It should be nearly impossible to pull a hose off a barb fitting even without any clamps. Pump pressure should certainly not be able to do it.
If you are continuing to have the issue, it sounds like either your barb fitting is not properly matched to the tubing size, or the tubing has aged and "flared out" over the barb, coming loose over time. If it's the latter, just cut about 2" off the end of the hose and reinstall. That may fix it.