There are lots of marinades you can use to enhace the flavour of your BBQ meats, but if you want them to come out tender rather than mushy, it's best to go with salty over acidic (which is why you should skip bottled salad dressing).
Think soy sauce-based marinades or salty dry rubs versus marinades that are primarily vinegary or lemony.
The video above, from the Insitute of Food Technologists, explains the science of this, as well as other BBQ facts. Essentially, if your goal is to just grill a very tender piece of meat, make sure your marinade's main ingredient is salty. Health-alicious-ness suggests, in addition to soy sauce, fish sauce, teriyaki and oyster sauce as sauces and dressings with over 20 per cent sodium content.
The Chemistry Behind BBQ [Institute of Food Technologists]