Hey James,
You must be doing something wrong cause a pump will last me a year easy.
A few hints to make sure your technique is correct.
1/ Make sure BOTH feet and hands are on the pump whilst you are pumping to stop and out of linear movement.
2/ Take your time pumping up and don't be too heavy handed.
3/ Get a good quality pump to begin with and look after it. Any of the aluminium shaft ones from Cabrinha, Airush or Slingy should be solid enough.
4/ Don't pump your kite too hard. 7 psi is about as hard as any kite should need to be, even this is way hard IMHO.
5/ If you do maintenance every few months on a pump it helps it stay in good nic.
If you're a big guy, buy a pump with the larger volume (longer stroke). It will prevent you from over extending on the upstroke and therefore pulling the cap off.
Hope this helps mate. Good winds,