You probably don't want to hear this, but trying to protect an investing idea with a contract is a long shot. If your partner wants to cheat you, there's nothing you can really do. All your partner would have to do is agree to your proposal about sharing profits, invest a little with you, then invest more money where you can't see it and you won't get your share of those profits.
If your partner is going to be honest, you won't need to worry. If your partner is going to cheat you, a contract isn't going to stop it.
If your partner is putting up the money, and you are contributing just the idea, you better get a lawyer to work out the contract. Don't cheap out. Because your partner with the money is surely going to protect HIS interest.