On a bright, sunny day last year, I walked to work in my favorite pair of leather boots. As I stepped out of my front door, I heard a strange sound. I spent several minutes trying to trace the noise, assuming it was an unwelcome pitch from my headphones or the busy streets of New York. Only then did I realize the sound was coming from the bottom of my own shoe.The persistent percussion was caused by a tiny rock stuck in the heel of my boot. It shimmied in quite easily because, to my surprise, the outer sole was filled with holes.I went to the cobbler, who informed me that the repair job would be $175 — $100 more than it would’ve been if I had simply looked at the bottom of my shoes earlier and known what to look for when I did.If you’re spending a lot on dress shoes, loafers, or boots, you should do everything you can to avoid a full resole, which can cost $250 or more, depending on the design and the brand.The experts agree: Just like with people, preventative care matters for footwear, too. The more damage you can avoid, the cheaper the prognosis. Here’s how to care for the soles of your shoes from the day you buy them, and how to know it’s time to head to the cobbler for a tune-up.