Wipe up the excess toilet bowl cleaner immediately using paper towels or a sponge.
Apply 1 to 2 tsps. of a stone cleaner to a damp sponge, and wipe the cleaner over the entire surface of the spill to remove any discoloration and to stop any etching that the acids in the cleaner can cause.
Rinse the sponge in hot water, and rub it over the marble to remove the stone cleaner residue. Dry the marble with a clean, dry cloth.
Apply 1 to 2 tsps. of marble polishing powder to the surface of the stain if the toilet bowl cleaner created a dull spot in the marble.
Fill a spray bottle with water, and mist the polishing powder lightly until it is damp.
Buff the area with a cloth until the dullness diminishes and you restore the shine to the marble.