I am agreeing terms with a new part time nanny to look after our 3 school age children (after school and in the holidays). She has asked whether we would pay her a percentage retainer (i.e. some percentage of hourly rate) for those hours when she won't be working for us but might need to be available (e.g. if one of the children is ill during the school week). Does anyone have experience of how this would actually work? What percentage would be typical and would I offset the retainer paid against any hours actually worked? All thoughts most welcome.