The drain in our bath gets clogged with hair very easily, so I started looking into options for preventing hair getting in there in the first place. The best solution so far seems to be the OXO Silicone Shower & Tub Drain Protector, which sits over the pop-up drain. It has a metal piece to weigh it down, and is made from silicone for a better seal. We have the OXO stainless steel squeegee, which works great. They give a lot of thought to their designs and make good products.
So I started thinking to myself - could I 3D print this? I couldn't find anything similar on Thingiverse, so I made a simple dome shape in OpenSCAD with a bunch of holes in it. The first prototype printed in PLA seems like it could work eventually. The PLA is too rigid to form a good seal, so it moves around and debris will get past it. Maybe a good reason to experiment with flex filament? I'll post the design here and on Thingiverse once it works reliably.