In the picture below the crotch strap is just over the weight belt buckle, but I normally wear just to the right of the buckle. It works either way. If I just lift on that buckle the weight belt will fall and the crotch strap will not slow it down.
The first thing I do is put on my weight belt. After I put on my tank/ kit, the last thing I do is attach the crotch strap. I make the loop around the weight belt and close it with a snap buckle. I use a one inch strap with snap buckles that I buy at Wal-mart (they sell the same straps/ buckles in many outdoor stores like EMS, etc).
You may be able to see the snap (Fastek) buckle right on front of the weight belt.
You can do the same thing with the double ring type of buckle that Allan makes and sells. All you would need is the double ring at the end of the strap and close a loop with the other end of the strap.
I am actually now thinking about trying the double ring buckle type to replace the buckle that I am using. Either way would work just as well.
Here is a closer view. This is my old back-pack (what I was using a year ago) with buckles on the shoulder straps. The harness on my new back-plate is similar, but without the shoulder buckles.
Notes:
The little color bands next to my waist belt buckle are the Cozumel Park dive permit bands.
And yes, I wear two computers when I am on vacation diving three, four, or more times a day. I don’t want to loose a single dive because of a computer failure.