When I first started I lamped on a slip, then trained the lurchers to lamp off the lead, hard work at first but perseverance paid off, then worked them off slip all the time, using a hiss to send the lurcher.
Always like a lurcher well trained in day as well, for ferreting and mooching, retrieving a must day and night, anyone tells you different aren't capable.
my two will lamp off lead i never even taught them they just done it but as for retrieve its no chance,some dogs obviously wont do it as i have tried and better tried to learn them and they show no intrest what so ever i would much