Is there any way to include grid lines in your finished map so they display on your unit?

Not really. You can include grid lines along with the "Frame and scale" option when exporting in image formats, but this isn't so useful for displaying on the unit. Is it not possible to configure the unit itself to display grid lines?

I've divided my large lake into multiple sections with one project per section so what I was actually looking for is a way to display the borders of each section on my finished map. Any ideas?

The simplest thing I can think of is to create a new polyline or polygon layer and draw a new object to represent the border.

Perfect... thanks Matt