I have chemistry puns that have to do with the elements, for example policemen=copper or cu. I need help on some of them I cannot figure out, thanks!

1. What a sales clerk does with items in a store
   
2. To pick up a heavy box
   
3. What you get if a truck runs over your legs
   
4. Two equally hairless men
   
5. to fix the dike (river retainer) ... I have no idea what this even means