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Hiring from your own and employee's network.

Provide significant referral bonuses to employees and ex-employees if a new hire stays on board for more than 6 months with above-average performance reviews.

Run evaluations with external recruitment firms - do quality shoot-outs with three recruitment firms for the same open role - each may present only three CVs. Never run any position with less than two external recruitment firms and let them clearly know that you're tracking quality metrics (CV fit, interview quality of candidates, job role fit, and six month retention and above-average performance review) and will retire your partnership if they drop below mean.

Run an empanelling process for the recruiters for each role and learn how to do it properly and repeatedly. This is a simpler process than the one you run internally with the hiring exec (you?), hiring manager and interviewer pool. You have an empanelling process, right?