I have smaller pens built off of my main pens and have a building in each pen with an alley way going to the door. I just walk in through the building into the pen the deer walk around to the alley way and walk right into the building. You do want tame deer and have sight barrier around the fence. We had a bottle raised buck fawn that we bought about 11 years ago and we had to keep him just for the scent collection because we couldn't part with him. All you had to do is walk in the pen in the evening and clap your hands and he would walk right into the building. We lost him this year it was a very sad day to say the least. The main thing is give them some treats inside the building or bottle feed them in the building if you plan on using them for scent collection and you won't have any trouble at all. Most mornings when I open the doors to let them out to clean the stalls. I have to go in and get them up and run them out of the building so I can clean them. If I leave the outside door to the pen open they will actually try and walk in the building while I am hosing it out which is 8x8 feet. If it is done right there is very little if any stress on the animals. I think some like it better because they get special treatment and lots of treats.