Don't you just love it when some one says "its not an option" and what they get back is, "yes it is, do it this way..."
Maybe.
Loctite makes a whole range of threadlockers, grouped both in colors (red, blue, green, ) but also with numbers, llke 242, 271, etc. Red 242 and Red 271 are NOT the same thing, for example. Each one is intended for a particular type of application.
Some threadlocker products are intended to hold and be unscrewed when needed. Some require some heat in order to remove the screw or bolt. Some are made to be PERMANENT, and those are dammed difficult to remove.
SO, please, don't just "use the red one" do some research and see which one the company recommends for what you want.
I've had good luck with a product called "Guntite" it holds everything I've tried it on, and doesn't need heat to remove, just a correctly fitting tool.
I'll admit, I don't have a scoped Ruger with Ruger rings, so I can't say for certain, from personal experience about that. But everything else I've used it on has held just fine (including the recoil rods of my Auto Mag). The key to having a threadlocker hold properly is to degrease the threads, before using it. Remove all oil/grease from all the threads, using the proper solvent. Then add a drop of the threadlocker per mfg instructions, assemble and let set.
This has worked for me, I expect it would work for you, too.
Good Luck!