At the start of the walk, the walk leader should:

1. Appoint a back marker, preferably an experienced walker who can map-read.
2. Check to see if everyone is suitably attired and seems physically capable of handling the expected terrain.
3. If someone is obviously ill-prepared, firmly but politely tell them that they may not take part.  The decision is that of the walk leader, not that of the person    concerned.  This applies especially to Hard or Strenuous walks where such a  person could put others at risk.
4. At or near the start, arrange a head count of participants.