Bookings

Hi all, we are starting to use Bookings for our company. We have several staff providing the same service. When a client goes through the process of selecting a service, they have the option of choosing the available staff members, but also 'anyone', which puts the service in another column belonging to no one. This function allows the client to choose a booking time that no staff member is able to accommodate. Is there any way to turn this function off and only allow available staff members to be selected for the service the client is interested in? Thank you.