Personally, I think it is almost impossible to keep eyeliner completely smudge-free! Especially in the summer.
My advice would be to buy the pencil kind, as opposed to liquid. I use Wet and Wild. When you are done applying, take a Q Tip and clean up underneath to start out fresh. Then, as the day goes on, just keep on touching up with a Q Tip (it works best!).
Also, I find that if i only put eyeliner on the tops of my eyelids and the bottom corners of my eyes, there is less smudge.
:)