Pha's protection, chameleon skinks, intervening units, Lord Kroak(with -1 to hit mask), enfeebling foe, net of amyntok. The possibilities are endless. Well, not really endless, but there are lots of possibilities. P.s. I'd be more concerned about an empire gunline or wood elves with trueflight arrows than leadbelchers.
Another good one is using high magic spell tepmest and heavens iceshard blizzard and curse of the midnight wind.
The usual skink cloud is more absurd than leadbelchers. Leadbelchers have a pretty clear disadvantage, which is easy to exploit. They are standard Ogres, which mean T4 W3, and only light armouor. Even without poison, they are relatively easy to wound, and no armour to stop those wounds. they are slow to fire, so they can't stand and shoot, if you ever get in position to do so with a monster. remember they are monstrous infantry, so rippers are pretty useless here, because KB ceases to work. Furthermore, they are only BS3. Even if they ignore multishot and move and fire penalties, even small modifiers screw them over.