No matter what you do venison is not going to taste like beef.
If you have tried alot of marinades and still nothing works you should try using a crock pot and cook for 8-10 hours using onion soup mix cream of mushroom soup and 1/2 cup of milk. The creamy suace helps mask the concentrated flavor of the venison. This is very good.

Another excellent way to hide the venison taste is to cut venison into 1 to 1 1/2 inch chunks(pieces) and marinade in teriyaki sauce overnight then wrap a half slice of smoked bacon around it and secure with toothpick. Broil in oven until the bacon is crispy(to you liking). I have served this to many non-venison eaters and they love it. With the combination of the bacon and teriaki you can not tell it is venison.
Good Luck