RE: Judging Yardage
As far as 3d shooting this won't be much help but when it comes to hunting- I find about 4 softball size rocks and spray praint them white in the off season, making sure to give the paint months to dry and time for the scent to disperse. When hanging stands, about a month or so before the season, I'll place the rocks 20yrds due north,south,east, and west of my stand; making sure they are visible from the stand. It's been my experience that it doesn't bother the deer at all they hardly seem to even notice them if you place them out well before the season. It gives you an easy reference point when the big fella steps in your shooting lane.