I have/had this issue with my scout as well. I've done a couple things:
The holster is attached to the boot with rivets, right? Well I've actually got a few layers involved here. From outside-in: Holster-boot-elastic-curvedABS. This keeps it together, and then the elastic is an elastic strap (leftover armor strapping) that wraps around my leg and attaches to both itself and my suit with velcro.
Hope that helps!