Knife, either slice the throat or puncture the lungs. I carry a Sog Seal knife in my car and when I hunt just for that reason. A K-Bar or something simular would work as well. I have had to do it a few times. I walk around the deer and aproach it from the back side (opposite end of the feet, not the butt) that way I can't get kicked. I walk up calmly and put the knife thru the lungs and back up. Only takes few seconds. Then I wait for the deer to expire. Not a pretty sight but it works. Same thing that happens when you bow hunt, you just don't always see it.

The reason I use the larger knife is because I know It's long enough and sharp enough to go thru both lungs with a quick poke to the hilt.

If it's on the side of the road you can call a sherrif and they will do the deed with shotgun or something sometimes.

If a deer doesn't get up and run when you walk up it doesn't have a whole lot of fight left in it, or energy. I have drug injured deer off the road while still alive and they didn't have the energy to hurt me.

Paul