Review and beefing up of subcontractor contracts

We're an established pet care company, using subcontractors who, though they often carry out other work, do the majority of the pet care work through us. Sometimes these contractors have begun to work for themselves and have approached clients directly. We do have a contract in place but we feel it needs beefing up to protect the business.

As well as these existing relationships, we're hoping to expand the business by working with other small established businesses (bona fide subcontractors) who will already have their own pet care business - generally just one man bands - but who have spare capacity. This will enable us to expand our geographic offering. However, we need something, based on our existing contract which will work for these relationships. Again something that will hopefully prevent colleagues poaching clients.

We're aware nothing is going to prevent this from happening, but a contract with teeth and an idea of how we would enforce it if required would provide some security.