If you have rivets I see a simple solution. Put a rivet at the edge of the beard and retain the back strap.

I will show you how I did it with my sheath for the rattlehawk. It doesn't show the retention strap in place.

It has to tilt and the spike comes out first so it will only rotate out one way. I know Mashed Cat has way more experience with building than I but it has worked for me so far.