Include an enforceable and valid restraint
By building this into your employee's contract, should an ex-employee poach clients or steal confidential information, it will be a breach of their contractual obligations. If you ever need to rely on it to enforce a former employee’s obligations, a court will consider the reasonableness of the restraint at the time the contract was entered.
Broadly put, restraint of trade clauses are enforceable to the extent that they are “reasonably necessary” to protect the “legitimate business interests” of the employer. The law will, for example, protect an employer’s trade secrets, confidential information, customer connections and staff relationships. However, the law can’t protect an employer against simple competition from a former employee.