A coffee can with kerosene under each leg would probably do the trick if water down not. I've heard that people in NYC did that during the Great Depression to prevent roach infestation in their apartments.

My grandfather always put some type of tar around the trunk of a couple of spruce trees on his lawn to deter the carpenter ants, it was thick and rubbery, like a mix of tar and pitch, he wouldn't have been one to use poison. If I can get to him on a day that his parkinsons is mild I will ask him what it was... Seems as though it could work well for your application.

Stainless steel legs or some other metal legs I imagine would work good as long as they aren't brushed. Wood is easy for ants to climb, grease wouldn't do a thing for you with ants, but metal should do the trick. If not make your own termite guards to put around the legs or do that to start with that will keep the ants from crawling up the legs.

My brother in law manages a vineyard and suggested duct tape sticky side out, around the legs. He uses it to prevent ants from getting to the grapes and around the base of other fruit trees. Similar to your masking tape trick, it may work, give us some feedback.