Probably smell it when their buddy poops it out and then drive the other deer crazy trying to find it. Seriously though, most can smell it quickly further than you will think. Kind of makes you have more of an appreciation for how good they can smell. keep an eye for any signs of dampness or mold on corn or anything else exposed to moisture. Those toxins are dangerous to animals. I had a 40 gal feeder flood one time with the corn starting to rot before I could get back to it. Luckily the corn would not come out and the feeder stop working. Talking about some nasty mash. I pulled it out of the woods and cleaned it out. I would mix in some better feed like roasted soybeans or peanuts to give them some extra protein, especially in summer and fall to help with overall growth including antler growth. May want to add some salt or mineral blocks to the area too.