Vinny's Allotment Plot

That's lovely and you could do that by turning your rectangular plot into 2 triangles with a diagonal path from one corner to the opposite corner.(along the hippopotamus)
I'm a fan of paths like that. Or you could split that into 4 triangles with an X path.

.............and its a stringchalkbod.

I used to use a stringline with chalk for marking out steel plates in my engineering days. Always flick the line twice to make sure it was straight.
Marking stuff out on the plot I would use a stringline and you could use flour, or for a more permanent line a whiter aerosol.