[koonsolo]

Working in the weekend without pay seems like a problem of your employer and not you. By asking "can you work in the weekend because blabla" he puts that problem onto you. The trick is to point the problem back to him. For example you can say "seems like you need to hire another person, is that planned already?". Or "You need to put a better planning in order" etc.

Try to get concrete plans and dates out of him, and then use that as excuse to not do things "we agreed you would hire someone else at x, you didn't do that, and now I have plans for the weekend. Better make work of that soon!"

He will always try to find excuses, but try to steer the problem to him. Because in the end, it is a failing on his side that you need to work in the weekend, make it very clear it's his fuckup, and if he doesn't fix it soon, it will be him in shit and not you anymore.