Everytime I ask people to put a coaster under their glass of water, I feel like I'm pulling a Monica (from Friends) and that sucks. My hubby even says why bother? the table is full of water stains anyway. But to me, if you can prevent - prevent!
Now, segway...check out these cool vintage record coasters from Elsewares! They come in a pack of 6 and are sealed so that water does not go through.