One way to dispose of the MEKP would be using it up! If you catalyze a batch of polyester resin use half brand new and half old MEKP. Even if the old MEKP has decomposed and lost 20% or so of its strength it should still work ok.

In several EU countries you can anonymously get rid of dangerous chemicals and waste, without having to pay for it or having to identify yourself. Where I currently live collection trucks with trained personnel come to every town once or twice a year and you can drop off whatever nefarious stuff you have in your possession. Just tell them what it is, ideally it's still in its original packaging with labels and they will take care of it, free of charge and no questions asked.

If that's not possible in your location and you don't want to risk using it for parts or moulds then it can be soaked up in wood dust or similar absorbent material and burned in small amounts, with lots of wood.

I've never had to dispose of MEKP, as long as it's sealed, it should be fine

The answer is easy, make a small batch and see if it works or not  

Hi, I have some MEKP catalyst which is 3-4 years old.  Is it safe to use this in a new project or could it have "gone off" and thus ruin my project.  MEKP is cheap enough so if there is any risk it won't work and I need to buy some more then that's ok.  If I do need to dispose of this MEKP, what is the recommended way of doing it?  I know MEKP is really nasty stuff (I belive it is about the nastyest chemical used in composites), so want to make sure I dispose of it properly and safely.

Many thanks, lee.