How can I keep my peel and stick tile from popping up? I've tried sticking more glue on the back of the tile, but that does not work. It is being put on 1/4 plywood subfloor.

What type of glue are you using? Are you using a new piece of tile?

FYI, they make a primer designed to make those self-sticks stick better - check it out at Lowe's, HomeDepot, etc.

You can try contact floor adheasive. This is used with vinyl composite tiles.
Also renting a flooring roller and roll the entire floor surface to make sure all tiles are stuck.

Sometimes those tiles just won't stick no matter what you do with them. Maybe there is something on the subfloor that's causing it not to stick. Try another one and if the same thing happens then there must be something there underneath. If you try too much stuff to keep it down you'll just have a big mess that will show from the outside. GOOD LUCK!

Never have been crazy about peel and stick tile.
Even if you do get it to hold up to everyday traffic, just try sliding a refrigerator out to clean behind it and see what happens.

Although they do make different grades though.

The person who ownes this housebefore me placed about a 4X3 area of peel and stick tile by the basement door, it started to slide apart, and since it was brown, I just tacked it down with some small nails. That seems to have helped somewhat.

Of course, if your tile is white, you might not want a handfull of nails lacing all of your tiles.