On odoo 8, you forbid access to a field to all users (except configuration permissions) in that way:
<field name="date_deadline" position="attributes">
<attribute name="groups">base.group_system</attribute>
</field>
To create new group of permissions,
on odoo 8, you can create record for new category like:
<record model="ir.module.category" id="xxx">
<field name="name">Name of new category of permissions</field>
<field name="sequence">200</field>
</record>
You can create new records for groups permission on res_groups:
<record model="res.groups" id="hide_only_admin_see">
<field name="category_id" ref="XXXX"/>
<field name="name">Usuario</field>
</record>
On category_id you must write the ir_module_category you are creating / overridiing.
After this, you have to create a line on your ir.model.access.csv to give correct permissions to the model you want, something like:
"access_project.issue","project_issue access","model_project_issue","hide_only_admin_see",1,0,0,0
Finally, go to the line and override like:
<field name="date_deadline" groups="your_custom_module.hide_only_admin_see" />