I've got a pair of Keen hiking boots that, at their best when brand new, never had a particularly good grip, and now, a few years later, have simply lost any grip to speak of. They are so slippery on any surface, wet or dry, that not only is it embarrassing, but downright dangerous sometimes.
My question is whether there is some technique or trick to getting the soles grippier? Perhaps scarring them with a blade, or running a grate over them, or some other method? The bottoms appear to be the standard rubbery type of bottom that most hiking boots have.