Here is the best marinade I have found. The whole idea is that the milk pulls out the wild and musky taste. The best way is to take 40% + Whole buttermilk and fresh rosemary, put in a foodsaver bag and suck all the air out. Place in the fridge for 48hrs at least. DO NOT ADD SALT OR WINE OR VINEGAR! Especially if you use a slow cooker as this will intensify the acid in the meat and can spoil it. I have had heated arguments with people about this, but I have been testing this recipe for years.
Now, I didnt say you cannot use wine or vinegar...i have done it in the past. But, for cooking purposes you add the wine toward the end. The vinegar is just not one of my favorite to be honest but some swear by it.
As soon as I kill a deer, on the way home I stop and get a gallon of the highest fat content buttermilk I can find, and luckily I get it at work! Os soon a the meat is cleaned it goes in the buttermilk. I also sometimes will put cumin, white pepper and cayenne in if making fajitas out of the skirt and flank. More of that later.