Some marinades are more tenderizing than others. Accent is a meat tenderizer (it does contain MSG, though so if you're sensitive to it - if you've eaten chinese restaurant food, you probably would know). Another tenderizing ingredient that breaks down the fibers in meat, making it more tender is pineapple, but it has to be fresh or frozen to work better than wine or other acidic marinade ingredients. Kiwi might work too, because I know you can't add either fruit fresh or frozen to jello because it will never set (because it breaks the protein connections that makes the jello gel).
You might try Google or Ask.com to find meat tenderizing tricks. Whenever I have a cooking question, I can usually find the answer in a few minutes this way.