I would suggest a little color correcting in addition to the concealer. Depending on the color, you use a concealer the opposite color of the scar. If they are red- green, purple- yellow.
Nyx has good concealers and they are cheap.
If you are going in the water I would suggest, an industrial barrier spray, mehron is also good because... Amazon and it’s cheap. But i would suggest Blue Marble setting spray, that stuff works super well. It is water proof, sweat proof.
Mehron Makeup Barrier Spray (2 oz) https://www.amazon.com/dp/B00FE94PQ2/ref=cm_sw_r_cp_api_i_WYx3CbAKWVY70
If you are really interested in covering stuff, liquid latex works really well. It blends into skin really well. A little search on YouTube will have hundreds of tutorials for latex.