How do I stop punctures for good?
There are a few things to do. I'd start by reading this link from Sheldon Brown.


First determine how the flats are occurring.


Inspect the tube. Is the rim tape on the rim properly? (if not, you'll see a puncture on the wheel side)
Is the tube being pinch flatted? (a snakebite flat, two very closely placed punctures - usually a sign of too low pressure)
When you re-install the tube, are you pinching it between the tire bead and the rim? (You can make a rolling motion over the rim with the tire after its seated to prevent this from happening).
If you can't find the puncture easily, pull the tube out of the tire, give it some air and then try to find the hissing. If you can't find the hissing, try passing the tube around your lips or dunk the inflated inner tube into water.

Check the inside and outside of the tire for any embedded debris, carefully. If you find some, remove it. 
If the tube doesn't have any punctures, is the valve good? Sometimes a faulty valve causes pressure loss. You can either re-core the valve in some cases, or more easily just buy a new tube.


Many manufacturers make kevlar belted tires which have stronger puncture resistance (such as the Schwalbe Marathon Plus), but if your punctures are happening due to rim tape or something, then its not going to help.

If you are running such big tires at 55 psi though, I don't think it's low tire pressure -- I've had about 300 pounds of stuff (bicycle, rider, cargo) on a bike with 26x1.9" tires at around those pressures without any problems on some pretty shabby roads.  

If the first flat was indeed a puncture due to debris, my guess is that you didn't actually get all the debris out.