Fact is nothing is all that hard to remove, just look at some of the forums where people do it to see what is inside... I have see people grind away epoxy with wire brushes layer by layer with a dremel tool, or use a heat gun and dental picks, and others that can't be bothered with slow labor, and don't mind the safety issues just jump right into the good ol' fuming nitric acid that eats away epoxy painlessly even on commercial IC chips... Trust me a few bucks to purchase the fuming nitric acid is well within the means of anyone that desires to see what makes it tick inside... You are just basically keeping the honest, honest, not actually stopping or hindering those that want to crack it...
Yes, over the counter 2 part epoxies will fail under heat a lot easier then commercial solutions, but many of the commercial solutions require precise baking profiles and/or uv exposure profiles... I have looked at a few commercial solutions myself and found most of them out of my $$$ range or too complicated (impractical) for the DIY user...
What I have found best, is to get some HIGH quality UV cure or 2k epoxy paint (they sell it for sign making as well as RC planes where the 'nitro' fuel dissolves just about any other paint) Get this in black, or deep green and give the board a nice once or twice over... Then you can use even a translucent or solid over the counter potting epoxy, as being opaque isn't all that important once you camouflage it underneath with the paint... You can even just tint clear with some black pigment (easily obtained from any fiberglass gelcoat company) and get it plenty opaque as to not be able to identify what is inside... Wanna get real fancy, now that the circuit is pre-coated with the epoxy paint (aka no risk of shorts) as I suggest, mix in some hobby glitter to your potting epoxy that you pour over it, to really make it pretty, and impossible to see through...