The tool you have heard about is the Garmin Fenix wristwatch. It has mapping software and a “project waypoint” function - as you say, point it at deer, enter distance from rangefinder and it places a ‘pin’ on the location.
I have one but prefer to use the NZTopo50 app on my phone, because the screen is so much bigger and the map more detailed. Works much the same way - point phone at deer, drag until the blue label states desired range and hit the “create” button.
Bookmarks