fields_security/views/sale_order.xml

<?xml version="1.0"?>
<openerp>
    <data>
        <record id="sale_order_form_view" model="ir.ui.view">
            <field name="name">fields_security.sale.order.form</field>
            <field name="model">sale.order</field>
            <field name="inherit_id" ref="sale.view_order_form"/>
            <field name="groups_id" eval="[(6, 0, [ref('group_restrict_fields')])]"/>
            <field name="arch" type="xml">
                <button name="action_quotation_send" position="attributes">
                    <attribute name="invisible">1</attribute>
                </button>
                <field name="client_order_ref" position="attributes">
                    <attribute name="invisible">1</attribute>
                </field>
                <field name="origin" position="attributes">
                    <attribute name="invisible">1</attribute>
                </field>
                <field name="fiscal_position" position="attributes">
                    <attribute name="invisible">1</attribute>
                </field>
            </field>
        </record>
    </data>
</openerp>