The best way to do this is to set your vesting date as early as possible. Once your stock is vested, they can't take it away from you without your consent.
During a sale can't the company just dilute everyones stock and redivide the new stock amongst whoever is still at the company? That way anyone who is not present at sale time gets a very diluted stock. I think this is why if you leave the company and your vested you still get much less percentage of a company than you theoretically should have. I would think this is the norm?
No, but they can create new stock. Or give some sort of bonus/better conversion ratio only to holders of preferred stock (VCs), with bonuses for current employees. Or...
