The LaRue customized Harris with the integrated picatinny mount is the way to go. It won't loosen like the standard Harris sling swivel mounts.
If you want a semi permanent install, a standard noch-leg swivel Harris bipod on a standard sling stud works well if you use a little loctite, but zi'd still recommend the LaRue customized Harris for the long run.
Short is best for bench tables and 20 round mags, Medium height for tall grass, 30 round mags, or downhill slopes. Pickup an accuracy 1st rear sandbag from LaRue while you're at it and learn to shoot with a rear bag.