It depends on what you are doing. My Patagonia Mixmaster pants seal really well around my boot tops, so a length of shock cord is all I need most of the time.

For times when life isn't so easy, a pair of OR Crocodiles (or Expedition Crocs) is usually the solution.

If you climb in crampons a lot, I suggest smearing Seam Grip or something similar over the inside ankle area of the gaiter to add some durability. It will help keep any tears from getting worse if you do poke a hole. Also, ice and rock will wear out instep straps quickly, which is why I like using shock cord on my pants. It replaces quickly, for a dollar or two of cord.