Easy and cute; I found this idea in a catalogue. They were selling these for like $20! No bueno. So we whipped them up in our creative corner at the nursing home I work at.
Take your clay pot and paint the bottom blue, red, or whatever other color you imagine a men's shirt to be. Paint the top lip white.
Cut out two triangles from a white piece of foam. Cut out a tie from a piece of fabric. (I Googled the tie template I used.)
Glue the white triangles onto the white lip of the pot on either side of the tie you've made. Voila! A gift for Dad!