Some how the medical community has figured out how to enforce......every one I have been to since this pandemic began....big signs....MASKS REQUIRED....NO MASK NO SERVICE...with someone at the door taking temps/asking questions.....if someone does not have a mask they are offered one....if they refuse they are asked to leave (I witnessed such a couple of times already).
Just like some big box stores have folks sanitizing carts they can also assign people to the doors.....no mask....no enter.
No army required.
Yes there will be, as always, some grouchy old fart challenging the system....easily handled by store management....just like Costco does......in fact here is one now
Woman Sits on Floor in Anti-Mask Temper Tantrum | NowThis - YouTube