Your contract needs to state something along the lines that the client is responsible for the obtaining of any neccesary permissions for any/all commerical uses of the photos including but not limited to model & property releases and that they, the client assumes all liability for their use of said photos (good for situations where you can't go and get a release from a boat load of people).
Something like this maybe (it's an excerpt from my p.i. contracts):
I, We, Our, My heirs, beneficiaries, devisees, legatees, administrators, and assigns further agree to protect, indemnify, defend, and hold harmless said investigative agency, it’s owner, and/or its agents and authorized employees from any and all actions, causes of actions, claims, costs, damages, losses, liabilities (including actual attorneys’ fees) and demands of whatever type, wherever situated arising directly or indirectly from their investigation or use of information obtained through said investigation which I, We, have requested above.
Edited for photographer use:
The Client aggrees to protect, indemnify, defend, and hold harmless "YOUR COMPANY NAME", it’s owner, and/or its agents and authorized employees from any and all actions, causes of actions, claims, costs, damages, losses, liabilities (including actual attorneys’ fees) and demands of whatever type, wherever situated arising directly or indirectly from the Client's use of the photographs supplied by "YOUR COMPANY NAME".
And here's an excerpt from the one that came on the Photographers legal handbook (I think that's the title - and it's not as "wordy" as the one made for my p.i. contract):
Client Liability
Client assumes full liability for its principles, employees, agents, affiliates, successors and assigns (including without limitation messengers and freelance researchers) for loss, damage or misuse of the Photographs. Client shall indemnify Photographer against all claims, liability, damages and expenses incurred by Photographer in connection with any third party claim arising out of use of said material hereunder.
And if you are just worried about them using the photos in the future for things not specified in your original contract you just throw some line in their about any useage not specified in your agreement must be negotiated with you prior to them doing it.
Of course when in doubt always have a lawyer go over your contracts (of course that won't protect you from being sued, it just might give you some piece of mind and maybe catch some loop holes in your agreements).
