We have a sign up schedule in our school for our COWs (Computers on Wheels).  Teachers sign up for a morning or an afternoon to borrow the cart.  They are allowed 2 slots per week.  Custodians are provided access to the sign up list so that they can move the COWs to the appropriate classrooms (end of day or midday).  This seems to work well.  This year we are rolling out 1-to-1 in grades 3 and 5, so mainly our 4th grade teachers are borrowing the COWs.   (Last year the COWs were used daily by grades 3, 4, and 5, but I imagine they won't be as busy this year with our 1-to-1 roll-out).