I just ended up getting WeatherTech Digital Floor liners. I had the OEM mats and fancier aftermarket rubber mats - eventually, they dripped or leaked, made a mess of the carpet. Unfortunately, they are pretty pricey - but fit literally like a glove and have sides deep enough to trap a significant amount of water, slush, winter-time nastiness, etc. Couldn't be any happier - well made (made in the USA) and flexible even in the coldest nights.
I've seen some people use those self-adhesive floor liners - like the ones they use for construction - sticky side on carpet, so that they protect it from any spills, dust, etc. Only thing is, you have to make sure the mat doesn't get soaked through - the liner will prevent it from leaking down to the carpet - but the floor mat itself will just sit in some nasty juice until it dries out.