It is a very good idea, making things clear to the PH. In a nutshell, my advice to a PH is that he fires only in a life or death situation. Other than that, if he shoots, he shares the cost of the trophy.
There is another side to this coin. I have a video, passed on to me by an agent, where the client literally pleads with the PH to back him up on a tuskless cow. The PH declines and tells the client his gun is ,big enough' for the job. The end result is the client shoots the cow in the trunk, from about 20 yards away, and she she walks away, a salvo of several shots are then fired into her rear end in an effort to bring her down.It is a most unpleasant sight.
M