NDA / Non-compete Agreements

Firstly, apologies if this is in the incorrect forum. Wasn't sure whether to put it in here or Legal, but felt that many people here may have first hand experience with such an issue.

I work freelance and recently my workload has increased to the point were I'm considering outsourcing some work to subcontractors to reduce the strain, while keeping clients. This is something I've only done with friends before and not on such a professional level.

My question is, in the most basic way possible; How do I prevent subcontractors stealing my clients? I've researched it a bit and there seems to be two options; (1) Trust - which for me will be hard to do initially as I'm new to this and will be sourcing freelancers I've never dealt with before (2) Contracts - this sounds the more sensible option but I've read that it can often turn people off from working with you.

Any of you have any experience with this? I'd appreciate any sort of advice on this as, like I said, it's all new to me.