If its true that our skin cells totally renew themselves every few years...?

Question

and the entire body regenerates every 7-10 years...then why do tatoos not fade...how do the stay permanent when the skin cells change over?

Answer 1

The tattoo ink isn't actually in the cells (try inserting a needle into a single cell sometime), it's in the fluid around the cells.
Yes, your external skin cells change often. Skin cells are falling off all the time and being replaced by new cells. Your epidermis is all dead cells. It's the dermis, below the top layers, that is creating new cells to replace the old.
Not all cells in your body can be replaced though.
Your eyeballs won't change much. Your brain cells are the same one you were born with, you don't get new ones.
Blood is recycled and renewed more often than other parts of the body because the cells are worked so hard and age faster than say, bone cells.

Answer 2

tatoo ink is inserted into living tissue, the layer of cells on the surface are already dead, that is why tatoos remain, althought they do fade over time.