Your investment is secure as long as both parties keep their end of the agreement once the contract has been written and signed. Say if the job is taking longer than anticipated, or it's not turning out the way you hoped upon periodic reviews of the work in progress. If the client backs out and does not want to continue the work at any time during the job, what ever money is owed for the (duration of that time and work invested), will be owed.
In the case of this happening, a contract dismissal form will be filled out and signed by both parties with the agreed amount of remaining balance due for what was completed, even if you don't plan on using it; the person doing the job needs to get paid for their time and labor.
Sometimes change of ideas or plans may come up in the middle of a project, which will result in more time and money spent on the project; that is a rare occurance as long as the customer is solid in their plan and decision and everyone is on the same page before work begins.
In the case of misunderstanding or miscommunication through out the project, it's always good to refer back to the initial written agreement that both parties discussed thoroughly, so there's no mistake in what is expected from both sides.