Designing a Corn Maze...Need to "cut" letters into a farm boundary...??

I'm looking for some advice on designing a corn maze for a corn field in Iowa. I have the field boundary, and I would like to cut some letters into the field border polygon and then load them onto a mobile GPS for navigation in mowing. Does anyone have any advice on how to create letters into a polygon? I have tried it free-hand, but is impossible to keep things looking good....

Any ideas?!?

Thanks,
Bryan