Re: MOPS for shoulder & ribsHightower,
On Ribs I simply use apple juice or cider in a spray bottle. The rub and smoke impart enough flavor on their own.
On shoulders I generally mop every hour and a half or so with the following;
1-2 Cups Cider vinegar
1/2 can of beer
2-3tbs of Jeff's Naked Rib Rub
If you plan to mop, make sure you allow your meat to smoke untouched for at least the first two hours to allow a nice "bark" to form. If you mop too early, you'll just wash all that delicious rub right off into the water pan.
Hope this helps.