Men frequently pee in the corner of the stair/lift-shaft building on the top floor of the Victoria street car park. Perhaps the walls in that area could be painted with hydrophobic paint (brand name 'Ultra-Every Dry') that makes liquid bounce?
To find the location: Take the stairs to the top floor of the Victoria Street car park building. You will emerge onto the roof. Walk around the stair/lift-shaft building until you reach the only concave corner.