Homebrew PCBs

The good part about the water method, is that it lends itself very well to double sided boards.  

On the outer edge drill two small holes the size of a thumbtack.  You can use these holes a fudicuary marks and line up the mask and do double sided boards with ease.  Two holes in the board and two holes in the mask.

UV light
(Some part of tack sticks up here)
Mask
Circuit board
2 thumbtacks with the head of the tack on the bottom side