I had to fell some Siberian Elms on our farm that were taking over some of the open spaces. I knocked down a bunch of trees that were 6"-14" in diameter and 20'-40' tall. They still had a few leaves on them, and were pretty "brushy" in their forms. Consequently, when felled, they made nice, irregular "thickets" that were about 5-6' high, and the deer would be able to peer through.
I felled them just before the big rains, and only got back out to the farm yesterday since it had been so soggy.
It turns out that the deer absolutely loved their new cover! The hidden areas between the felled trees are absolutely covered with deer tracks. They have also made two big scrapes on the ground adjacent to the crowns of two of the felled trees. They even have an obvious licking branch in each of those crowns.
I wish I could make cover that immediately popular in my ponds for the fish - now that the water levels are going back up.