Using a sling in the woods: Oh, boy, this can be argued. I always carry my gun on a sling, barrel pointed down under my forehand. When walking trails, it generally poses no problem. If I come to a deadfall tree across the trail, I merely lift the gun barrel up with my forehand to clear the obstruction. If I am moving through brush, I may adjust the gun and sling so its weight is still supported on my shoulder, but the gun is upside down, and the barrel level with the ground. That generally puts the barrel about 4 feet off the ground for me.
For really tall brush, I either go around, or if I have to push my way through. I bring the gun barrel up, pointing skyward, and use the barrel to push through limbs and vines and branches. More often, I look for a hole where the deer went through, and bend over to go through the hole. Then, I merely point the muzzle through the hole, first, before I step through the hole. (I just practiced this procedure here at home so I could describe it correctly here. I apparently move my head down to the gun's barrel, more than I move the gun " up " to my face, when going through holes in brush. )
At a little of 6 feet tall, getting my longrifle through the brush is not my biggest problem. That is why I often go around thick brush. I tend to stick to game trails when I am going through the woods, because they are quieter walking. They also tend to go from one large tree to another, and I use them for vertical cover, so I can still-hunt as I go, sneaking a peek around the side of a tree before I move down the game trail to the next big tree. When approaching thick brush, I automatically begin looking for tracks and sign indicating easier routes around the thicket rather than going into and through it. I will throw a stick into a thicket if I think there might be a deer hiding in it.
The sling is there to help carry the weight of my rifle, on my shoulder, and not in my hands, so they are free to use to get over and around obstacles. I use detachable sling swivels on my guns, or use a hasty sling on my muzzle loader, which I remove when I reach a spot to stand. I also take the ramrod out of the gun and put it into the ground where I can reach it easily for reloading. I don't want that metallic clacking sound I get taking that rod out of the ferrules on the gun, nor the sweeping movement of my hands that occurs when I remove the rod from the gun, while I may have a deer in sight. If the rod is in the ground I can grab it, and reload behind a large tree with a minimum of visible movement.