Keeping a default resolution pixels/inch

I use PSE, and I like to have my resolution set to 72 pixels/inch for 100x100 icons. (I have no clue what the "standard" is, but I've used that setting for a long time and am used to it.) Sometimes, it changes automaticallt to 300 pixels/inch, and when I'm zipping along, I don't notice until I try to use text and it's ten times huger than it should be. Is there any way to keep it from changing when I don't want it to?