in behalf of is incorrect usage (Delete me if I am worng)
Depends on what your talkin about but usally onbehave
If someone is not available to speak for themselves, a person might say "on the behalf of *so and so* I would like to thank you...", or "on the behalf of *so and so* I am informing you...", or "on...
calf, giraffe, staff, and laugh
We will engage a solicitor to act on your behalf in your court case regarding drink driving.