I have had some success with decoys over the years, so for what its worth he are some things I have noticed while using them.
1) Bucks react to decoys better then does. Does accept a buck decoy slightly better then a doe decoy.
2)Have a buck decoy facing towards you and a doe decoy facing away from you.
3) Never put any scent directly on the decoy. I did this once and at the end of the evening hunt I put the decoy in a windfall so I wouldn't have to carry it out that night. The next morning there we deer tracks in the snow leading right up to my hidden decoy.
Also along with this if your leaving a decoy out over night dont leave is standing. If you have a buck decoy and leave it up there is a chance you will be picking up the parts of your decoy in the morning. Also a deer that never moves from one spot makes deer nervous.
4) The decoy must be visible to passing deer. I know that sounds pretty basic but if the cover is too thick and a deer never sees the decoy your just carrying extra wieght by bringing the decoy with you.
5) Add some movement to the decoy. I take the thins sheets of rolled up packing material and cut out in the shape of a tail then pin it to the rump of the decoy. Just a slight breeze will make the tail move. A small "tail flick" seems to relax deer investigating the decoy.
Hope some of this helps.
