LionDog- I use PURPLE LOC-TITE on some rings. A little dab will do ya- it spreads out a lot, as it's going in to a good fit.
I don't see the scope moving around on a AR-15 as a big problem. Places people talk about this a lot are Airgun Silhouette (those spring rifles tear scopes apart worse than anything- they reciprocate in recoil. First forward (!) then back, then forward... Spprrrooooinnnnnnggg.)
I shoot big bore handguns (well, just the little pups for me- .454 Casull and .357 Maximum) but folks swear by the rail sets made by JD Jones- who tries to get 3 or even 4 rings around a scope to keep it from shifting. You can spend $200+ on rings. I spend $45 for a nice Redfield set, and 5 cents worth of loctite.
You should see what some of us nuts are doing with the Savage MLII muzzleloader. That's the one expressly and exclusively designed for smokeless powder. It's proof tested to over 200,000 psi- so I want to hear no crap from anyone on this. If I blow myself up, I take responsibility. How about 250 grain bullets at 2600fps? Recoil is stout. Scopes do shift! Well... loctite 'em.
I was hesitant to do it at first, but my pistolsmith reassured me. He is an ex-AMU armorer, and a High Master shooter. His reasoning is that scopes are meant to be looked through, not at. So if you get a smudge on your scope, UNDER THE RINGS (fer gods sake), and that bothers you... then let your scope slip. The Ulradot is loctited in to my bullseye gun, hasn't budged in years of shooting. Why take it off if it works?
The scopes come off with no real hassle, the loctite flakes off. Epoxy will do the same.
If you want to use epoxy, I think it will do the same job.
TRY IT AND SEE.
Now you have advise from expert gunsmiths, and just some dude who it works for. It will cost you 5 cents to try it and see if it works for you. And if it works for you, it works for you. Personally, I won't spend $90 on rings.
If it works for you, it works for you. For me, my scope shifting is something I do not have to contend with, once my guns are tweaked in.
Pete