Why does my Lemon Merigue Pie split after it is cooled and how can I make my Merigue nice & high?

So here's what's happening. Heat causes expansion, cold causes contraction. When you let the pie cool, the pan beneath it, being metal (which expands and contracts the most to various temperatures) is shrinking, and the pie has to split to fit in the pan. One way to avoid having this happen is to use a disposable tin pie pan. They have ridges in them which help compensate a little for the expansion/contraction. Another thing that will help is if instead of taking it out the minute it's finished, you shut the oven off a little while before it's done, and you leave the pie in there. By doing this the pie will finish cooking, and then when it's done, you leave it in the oven, and it will cool down much slower. Also, you need to make sure that after you take it out of the oven, that you leave it out till it's at room temperature before putting it in the fridge. If you put it in the fridge while it's still warm or hot it will definitely split.