Elk Lake Resort (www.elklakeresort.net)  might be a good destination for you. Cabins allow pets, though not sure about the “run free” part. There is a beach, however, on the other side of Elk Lake that I know allows dogs off-leash. It’s called Little Fawn. Fishing is popular on the lake, as well as sailing, stand-up-paddle boarding and the like. Only other caveat is that until the Cascade Lakes Highway is plowed of snow, which typically happens around Memorial Day or later, you can’t get there except for on skis or in a snowcat! But for a summer destination, this one is great. You might also check out Paulina Lake Resort and Odell Lake Resort. Have fun!