From readiing this whole thread, I'd like to add my thoughts. Maybe Odielover was just asking a simple question about marking but Lorraine had some very interesting comments. Sometimes people don't know much so they don't even know what questions they should be asking. These posts are also read by many different people so even if more information is given than is asked for, someone else may gain from it.
Tail docking and spanking are two different issues. The docking is done at a very young age. Maybe it is cruel but have you ever seen the website that supports it?
http://www.cdb.org/case4dock.htm In some working dogs that are normally docked but weren't horrible injuries ocurred. Amputation was needed which is a lot more painful than the docking of new born tails.
Punishing your dog for marking may just make him more sneaky. Marking and spraying are habits and aren't necessarily broken just by neutering.