It does require a good amount of pelvic muscle tone and strength to keep it in, but it also is a "one size fits all," but we aren't all the same shape and size, obviously. You could use it in conjunction with something like this:
Bare As You Dare Harness. It's nice because it's so small, you would barely notice it.
I personally love my Feeldoe and have never had any problems keeping it in.