So what you're telling me is you can't promise me I won't leave with sand everywhere.

( which means she's going to have to rinse it off somehow before actually going back inside her own apartment. or his, for that matter. maybe she could leave something here, and then use that as an excuse to track back to his apartment to shower after a beach outing. then all the sand would be in his apartment instead of hers. now that's a thought. )

How about this: you promise not to put sand in my hair, and I'll promise not to track too much of it through your place afterwards?