runner's feet: any suggestions to make them pretty?

I've never been a runner at that level of dedication (and am now a short-distance walker, no more), but the fact that you routinely lose toenails suggests a visit to a doctor specializing in sports medicine may be warranted. The nail exists to protect the toe from impact, and when exposed to repeated impact like running, it shouldn't detach as a matter of course. It's possible there's some underlying cause or weakness that you might be able to address, from too much moisture in the shoe weakening the nail to how you hold your foot while running. (I had to retrain myself not to lift my big toes when my knees bothered me. I swear, it helped--but it hurt the toes and wore through the shoes, too.)

As an older person with a fingernail detachment issue, my doctor gave me the advice to clip close to the quick and file so there are no rough spots, moisturize with petroleum jelly overnight when they are not polished, and to keep them polished about half the time--or stop using keyboards. For toes, some of that advice might be apt. No typing with toes! Polish, besides being decorative, strengthens the nail and makes it flex less. Moisturizing allows it to flex and recover rather than start cracking.

Our daughter, who inherited her dad's ugly feet, swears by one of those electric foot sanding things to deal with calluses. I'm blanking on the brand name, but there's one main brand. She laughs that I still use a pumice stone and foot files. She uses it several times a week and afterward moisturizes with body butter for daytime, or petroleum jelly (and socks, if you like your sheets!) overnight.

Oh, and an aside: Among my summer shoes are sandals with a closed toe but open in strappy patterns on the rest of the shoe. (Look at Rockport Cobb Hill sandals. They have lots of styles, several with closed toes.) There's always disguises!