Could we have a tier form of treaties? Maybe one that you can go back on after 1 day and one you can go back on after 2 weeks?

Maybe also offer a ceasefire agreement/nonaggression pact where you don't allow their units to cross your land peacefully or otherwise.

What about a treaty that mirrors the time it is in place (up to 21 days). If I make a treaty with supercoolyellow and decide to break it 2 days later, then I can't attack him for 2 days. Or maybe a 2:1 ratio. Kept for 2 days, 1 day to attack. (round up) 3 days kept 2 days restriction.

A simpler solution might be to let the requesting player select a cancellation period (think unit purchase screens).

^win^

good call