Cooking sherry but delete the salt from the recipe because cooking sherry is preserved with salt (unless, of course, you like more salt). You can find cooking sherry's and cooking wines in your markets vinegar isle.
Sorry to a couple of the posters here, but chicken stock, vegetable stock, and regular fruit juice will not work as a substitute for sherry in a marinade because marinades for most meat recipes need the 'vinegar' base (fermented) that the sherry contains. Since the recipe says specifically to use sherry there's also a reason to not use simple fruit juice because of the flavor and tenderness the recipe wants to acquire.
As a sherry substitute you can use just about any type of wine or you can use red wine vinegar with 1 teaspoon of sugar or you can use white wine vinegar. You can also use cooking wines or cooking sherry's, but because cooking wine and sherry use salt as it's preservative you'll want to reduce or ditch the salt in the recipe for health sake. (08/12/2010)
Sherry is a fortified wine. Use dry to sweet-take your pick. Non alcohol, 2 Tbsp. sherry sub for 1 to 2 tsp. vanilla extract or use 2 Tbsp. of orange or pineapple juice. Your marinade will depend on the choice. (08/12/2010)
What I do, is use apple jelly and mix it with a little apple cider vinegar to make it more liquid. I have also used cranberries, mixed with some white vinegar and brown sugar. You need the vinegar to tenderize the meat so the flavour of the marinade can soak in. And taste your marinade before you use it, it has to taste good or it will ruin your meat! (08/12/2010)