Wrap your food in Heavy Duty (HD) aluminum foil and put it back on the grill to continue cooking.
This serves a couple purposes:
1. it focuses and distributes the grill's heat and the meat's internal heat back into the meat, causing faster, more even cooking
2. it collects juices, some of which evaporate and steam the meat, causing it to cook more quickly
It's a matter of personal preference. You certainly don't need to foil your ribs to make them pull-off-the-bone good.
If you do foil a piece of meat, you may want to put it back on the cooker unfoiled for a bit (15-30 min) before the end of the cook to firm up the exterior, as the steam action within the foil will soften your bark.