Ok, I had an interesting happening the other day. My light armor fighter found himself facing a phalanx-fighting group, all wielding heavy shields. After the mage provided some well-place fireballs and other area of effect spells, the archers eventually took him down. The healer was being grappled by their commander's wartiger. The next phalanx was approaching, and would require some cunning on the part of myself and the rogue. So, I grabbed a random potion, and hoped it was a potion of some cure spell. Downing it, however, I discovered it was a potion of Girallon's Blessing (Spell Compendium spell granting an additional two arms; the DM does not use the restriction for potions that they cannot be personal range spells). With my new two arms, I had an idea. I quickly grabbed two tower shields. Reading the description, they grant partial cover against three sides, but not all four. So, I grabbed two, placing them at opposite squares. I figured, that grants me four-way protection. Since attacks of opportunity cannot be made against a target who has cover, I figured I could move indiscriminately.
So now, to move! I quickly downed one more potion: Expeditious Retreat (I have two more arms, so it wasn't a problem). Then, I rushed around the enemy phalanx while the rogue held action for me to get into position. Once I was there, I attacked from behind. Since I was attacking with two tower shields, I had a -4 to hit (penalties stack). The rogue had done something clever. He held his action for the phalanx-fighter to move his shield. Being attacked from behind, the fighter did just that, positioning his shield towards me, instead. This activated the rogue's held action. The rogue had held his action to charge (this is a contended rule in 3.5, and my DM has decided that it is perfectly acceptable to hold an action to charge, but you can only make a single move action). The rogue slashed and killed the target. Anyway, as we began picking apart the phalanx, it came to bear that I needed to make a jump check. This is where the trouble started... what was my armor check penalty? -10 or -19? (-1 from magical chain shirt, -9 from each MW tower shield, or is it -1 from magical chain shirt, -9 from one MW tower shield?)
The DM rules -19, which was just funny. Still, I am curious.