Ninja man, a hand held range finder is as appropriate here, as it is with archery hunting. Bushnell has low to medium priced options and is very reliable and rugged. I've used most of them from high end Liecha, Swarovski, Leupold to low end $59 Bushnell. There is no need to spend too much and the Bushnell gets my thumbs up, for the lower priced fare. My wife inherited my first two over 15 years ago and they still work fine. Believe me, if you want a durability test of any hunting equipment, put it in her hands for a day or two. ;-)
Congratulations on your squirrel kills. Awesome job, combining stealth with your equipment and shooting ability. I like your style! Do yourself a favor, "bite the bullet", pardon the pun, and put a few bucks into a range finder and extend your effective range. I think as many shots fail because of poor range estimation as an unsteady hold.