well to be honest, I try to let them know before they get close to me
I have to have an organe hat/vets with me when ever small gam and archery over lap more or less, I found waving the orange works well from a distance, and MOST will go away from you
some however seem to think yu want company and to shoot the breeze with them, had that happen way too many times over the yrs

but if one should happen to get on me without me knowing so, I would whisle softly and get louder as needed

but to me, best deal is to get there attention farther out than on top of you if you can!
unless you want them close to get a good look at a trespasser, and then give them notice of the law breaking!, I do that now a days the most