mosfet failure reasons?

The load is basically homemade high frequency transformers, its all just for playing around and maybe learning a bit
But im expecting like 1-3 amps draw but it will probably vary alot, its being fed by a +/-12v supply I made
id also like to be cheap and make this with what I got already, an irf9520 and an irf540
I've never worked with pchannel mosfets or negative voltages before so this part is new to me,
Also the input will be square wave and the frequency will probably be as high as 500khz max more likely in the 1k-200k range