While the previous two posts are funny, the rules on thaumaturgy wards are very clear: they have to be stationary and built upon a physical/conceptual 'boarder'. A chalk circle, a threshhold, a doorway, etc. A moving shield can be placed upon an item, and the rules for that are well described. It can also be done with thaumaturgy.
While the previous two posts ideas are funny, they are bad form for a GM. Making your players feel/look foolish is rarely a good idea. Their characters should know the limitations of magic in advance and not be forced into looking like dummies. Brings back painful memories of my first high school Gm constantly prat-falling my first paladin. Almost always bad form to make fools of your players.