If the strings are moving between points, you are probably using either syn gut or multi-filament strings. Try using a poly string like RPM Blast or Luxilon Big Banger ALU Power. A cheaper poly option that I used to use is Volkl Cyclone. With poly, the strings will not move between points and will not break easily. But be careful. If you don't have good stroke mechanics, the combo of Babolat APD (very stiff stick) and poly is a recipe for tennis elbow. I had it.
Go for hybrids that either include Kevlar or Polyester if you're concerned about durability, they last a long, long time. If you're looking for feel, natural gut is the best. And always experiment with string tension until you find one that suits your play style.