Every redevelopment plan shall:
(a) Contain adequate safeguards that the work of redevelopment will be carried out pursuant to the plan;
(b) Provide for the retention of controls and the establishment of any restrictions or covenants running with land sold or leased for private use for such periods of time and under such conditions as the legislative body deems necessary to effectuate the purposes of this part. The establishment of such controls is a public purpose under the provisions of this part.