How to sculpt thin, flat surfaces?

i’m working on sculpting this mermaid and have run into a problem. how do i sculpt shapes that are flat and thin like the fins? when i try, i get errors where one side will go through the other. if i want to make it real thin it’s a lost cause and i keep having to settle for blobby versions of things like leaves and fins. (here’s another example with chikorita)

Enable the ‘Front Faces Only’ option in the sculpt tools panel