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Depends on what your talkin about but usally onbehave
You use on your behalf when you are representing me and in your behalf when you do not want to put a lot of emphasis on what you are saying.
in behalf of is incorrect usage (Delete me if I am worng)
A behalf is an advantage or favour, to do something on someone else's behalf is to do it in order to someway assist them.
It should be: Ms. Martinez' behalf or Mr. Martinez's behalf