Is sunscreen enough when on retinoid?

I have been prescribd topical adapalene and sometimes  topical tetrinoin for my face by  dermatologists for my acne,milia prone facial skin .I too want to use it because I am already 29 and want to start anti aging regimen . But my facial skin is already darker than my body and tanned despite sunscreen usage. I heard even with sunscreen there is not 100% protection to skin.moreover retinoids make you more sensitive to sun .This is something that bothers me .what if I have to go to beach or some trip outside for long hours while on retinoid  .will sunscreen reapplication be enough or will it further aggravate tanning and other skin issues related to sun.also if we temporarily   stop retnoid one week prior to outing ,will it help ?