The last time I did a couple of racks of ribs I roasted a whole garlic with them for the last two hours. I roast it on the rack above my water pan. I slice just the top 1/4 inch off of the cloves, extra virgin olive oil, fresh ground pepper and ground sea salt. As someone already said, leave the foil a little loose and the aroma will fill the chamber and add a bit of flavor to the meat. We served it with different crackers and sharp cheeses. Fresh berries go well with it also.
I also have rubbed the underside of my ribs down with roasted garlic before the dry rub. I used to do the top also but it was a bit too strong for some folks. We grow a lot of garlic so it something to do with the excess.