If t's locked by another user, you can not update a property.   Some ideas:

1) Use an agent that keeps retrying until it can obtain the lock, and then it changes the property

2) If the agent determines that another user has the work locked, it could send the user an email asking them to unlock the object.

3) Use a small enough timeout so users that lock the work and go to lunch don't tie things up for too long.

4) Design your app so users tend to review work instead of "perform"ing the work, particularly if they are truly reviewing and not doing something.  That way, they won't have the work locked unless they really need to.

/Eric