Couple years ago I hunted near a house where the owner would walk his lab every afternoon...on a lease and pulling that owner alone. I was set up in a ground blind as they would walk by 50 yards away. If I had a window unzipped as they approached and my scent blowing to that lab...he would smell me every time and he would go crazy wanting to come toward that scent...pulling on the lease. Now if I would have all windows closed...no scent escaping that dog would walk on past and never knew I was there. I saw this happen several afternoons so goes to show how well they can smell...and a deer can smell you better than that. Have seen them go on alert 200 yards away if they get your scent. Wonder we ever kill one.
