A sheriff is usually considered in most places to be the highest ranking police officer in their jurisdiction and can usually make an arrest on a police officer if they are required to do so.
Sadly though you'll very rarely see or hear of a police officer getting arrested when they do something against the law on the job.
Now if they were not on duty then they would get arrested by another police officer or sheriff.
Police officers are considered to be general purpose officers and they sometimes need the sheriff to come in and make a decision on some arrests.
In my area before a police officer or regular deputy that is not a deputy sheriff the police officer or deputy must have their supervisor show up before they can make an arrest.
The supervisor has to decide if the arrest is legal and the person can be arrested for the offense.