I have a quart can of POR15 in my fridge that's been there 5+ years and is still good. Place a layer or two of saran wrap over the opening before putting the top on to help seal it and reopen it the next time. Keeping it cold slows the curing process (considerably!). I pull it out occasionally to do small touch up jobs on my trailer and lawn equipment.
My wife finds it an asks me about it every year or so, and then I hide it in a different back corner.
