is a copy of the skype log or a screenshot enough to keep them from coming back at me if the game were to be succesfull? If not what should i have them do, Same thing for GFX artist (non pay).

You need to write a contract that states the terms of the arrangement clearly.

The best bet would be your lawyer - they specialise in making this kind of agreement watertight.

A cheap/simple alternative is to agree that your contributor will license their contributions under some well-known license (i.e. one of the Creative Commons licenses), the terms of which are agreeable to both of you.

This has the advantage that the licenses have already been written and vetted (by experience lawyers), and the terms of the licenses are well known, and conveniently described in plain English on their website. Even if you don't wish to open-source the end product, the CC Attribution or Attribution-ShareAlike licenses will allow that while giving you both some confidence in the terms of the agreement.

If you don't consult a lawyer or use an existing well-known licence as suggested above (I would recommend one of those options!) you can write your own simple contract:

• Do not attempt to use legalese or legal terms. These have specifics meanings you may not properly understand. Use plain, simple English.
• Keep it simple, and discuss it between both parties so that you are both happy and agree to the terms as well as what the terms mean.
• Be specific.

Check out the following posts from industry legal professional Mona Ibrahim for a good introduction to contracts:

1. What happens when you don't have a written agreement [part 1, contract basics]
2. What happens when you don't have a written agreement [part 2, real life application]

Again, if you really want to minimise your risk and do things as properly as possible you should consult a lawyer, but barring that hopefully this might help you to do a better job of writing your own contract if that's the route you want to take.

Hope that's helpful! (I am not a lawyer.)

If you both sign something which says flatly "X will receive no payment for their work. X is not entitled to any share of revenue or profit generated. X gives permission to use their work freely and without restriction" it's hard to see how that is unambiguous - legalese isn't magic after all.

Whether even a real contract would actually protect you I don't know. If you make the next FaceBook with their work you can expect to be challenged :)