I'm also into my watches and I can't not wear one, even for airsoft, just feels weird - so I just wear a very old Timex Expedition that I don't mind it getting beaten up further. I'd like to wear my Victorinox INOX, as that's literally bomb proof and more than fit for purpose, but don't want to fuck that up, weird isn't it haha.
So maybe another G-Shock, or the good ol' F91W if you're into your digitals.
Or, a G10 military watch, if you want the military aesthetic with some genuine military background - MWC will do you a solid example for about £70
Oh and stick it on a NATO!