It’s been ten years since an inflamed tendon in my ankle forced me to stop running for some months, and it was during that time I started using WordPress to replace the old static Web pages that had been here. After physical therapy, I found that the easiest and most effective way to strengthen my ankle is to wear a 5-lb. weight (except when running!). The worst one I tried came from the now-bankrupt Sports Authority, and the best I’ve used is the one I’m wearing now, from Dick’s Sporting Goods.
Three of the four reviews at that link are very negative. I’m only wearing one of the ankle weights, so if it starts to fall apart I’ll switch to the other one and assume it will last at least as long.