Animal Welfare Professionals

Hello,
I'm interested in learning how other municipal organizations in CA handle foster family agreements. Do you require foster families to sign a new agreement every time a new animal enters their home, or do you allow an initial agreement to remain valid for a certain period? In particular, for kitten fosters who we know will host multiple litters throughout the season, is it necessary to have them complete a full agreement each time, or have you found a streamlined approach that still meets legal and organizational needs? I'd appreciate hearing what processes have worked well for others.