Have you ever noticed how powerful those little plastic dividers are at the grocery store? There you are, putting your food on that little conveyer belt that flings your food towards the cashier spilling everything.
You thought everything was fine and dandy as you pick up the broccoli that toppled over the edge, when suddenly, a threat! Another shopper is placing their food on that same conveyer belt!
You quickly spring into action, and put one (sometimes two!) plastic dividers between your food and their food. On this side: my food! On that side: their food! Don't you cross that divider! I can see that bag of Oreos just leaning over the divider into my territory, almost touching my lemons!
I think this would be a great way to seal any border!
"Hey, lets try to sneak over!"
"No way, man! They've got those dividers up."
"Bummer. Hey, pass me the Oreos, will ya..."