Coverage for the absence of a staff member is usually a requirement stated in any organization's by-laws. That is, if you're on staff, your patients shouldn't go without care: you're required to make arrangements for these gaps of coverage. If you're familiar with the practitioners in the area, you can request from others on staff a reciprocal on-call relationship; if you're new, you can state that you'll be serving on committees that will allow you to meet others allied to your specialty so that you can make such arrangements.