i have a really big jar and i weigh pickles down by wedging in a tupperwear lid just the right size to fit into the jar, and then i put a little clay cup on top if it keeps rising anyways. i notice that larger jars are more likely to get a little moldy (which is ok, these are not bad molds, they can be skimmed off). smaller jars don't tend to do that, go figure.
i didn't think you were supposed to close the lids tight? I thought the ferments needed to "breathe" ?