How do you deal with ownership with investors?

If you are looking for capital or a merger/acquisition, how do you deal with ownership when there are investors?

E.g. if you are looking to sell a company, but retain some percentage of ownership, how do you make investors comfortable with you owning 2% of a $1MM company at closing and then owning 2% of a company that someone invests $5MM in then selling your 2% at that $5MM valuation? Is there some mechanism that protects investors in a situation like this?

(If there is a better way to phrase this question, I’m all ears as well)