Try a different *kind* of magnesium. Some kinds of magnesium cause that problem in me. I finally stumbled on a brand with 5 different kinds of magnesium and I can tolerate much higher doses of it. I know for a fact that magnesium citrate will cause the 'squirts' at much lower doses. Try magnesium malate--that is usually shown to be very beneficial to fibro sufferers. I take one that provides an effective dose of 825mg of malic acid once a day for 5 days only. I never take supplements 7 days in a row. Here's a quote from a health newsletter that I think may help you decide if you need more magnesium:

"Magnesium: An astounding 75% of the population is deficient in magnesium. Signs you may be lacking magnesium are: headaches, muscle spasms and tremors, menstrual cramps, kidney stones, heart problems (especially irregular heartbeat), and stroke. The way our bodies use magnesium is a perfect example of the way Nature establishes balance in our bodies. In fact, magnesium is Nature’s Calcium Channel Blocker. Calcium channel blocker drugs work to lower blood pressure by blocking the entry of calcium into heart cells and smooth muscle cells of blood vessels. Magnesium has protective features that balance out the negative effects of calcium overload on the heart. It blocks the entry of calcium into heart cells and vascular smooth muscle cells, reducing vascular resistance and naturally lowering blood pressure. Both minerals need to be present for the body to absorb them properly. The top food sources of magnesium to add to your diet are organic dark greens, alfalfa, sea greens (especially kelp), sea foods, wheat germ, nuts and seeds, and beans."

The magnesium formula I take is Nature's Plus and has magnesium in aspartate, citrate, aminoate, lysinate, methionate forms. I have very little trouble with my bowels while taking it, even in higher doses. I then also take the magnesium malate, so all together I get about 1075mg of magnesium/day, unless I feel I need more, for whatever reason, then I'll take another 250-500 mg of the Nature's Plus.