Way to try and stop people from editing what they should not on Contacts

We need to be able to restrict the fields that can be edited by anyone other than System Admins based on the Type of Contact it is. For example: for students & employees certain fields are populated from our Directory application, these fields should never be changed in 25Live. All other Types of contacts they should and need to be able to change all fields. I would like to have contact Source or Type I can create and then set and then restrict what fields can be edited on those Types. It would also help to have a Customizable HTML field that I would appear at the top of the Detail screen on an object when it is put in Editing Mode. That way I can give certain instructions such as is directing them to update in another place depending on the contact type and field.
For the second time I found a contact record where someone changed all of the info on the person to someone else and the only way I found out is by the username. They seem to do this when a person is replaced in a position.