You probably know about these, but for the benefit of folks who don't, you can forbid slice access and direct unwraps with clippy. Obviously this only lints your own code and not dependencies.

  - https://rust-lang.github.io/rust-clippy/master/#unwrap_used
  - https://rust-lang.github.io/rust-clippy/master/#indexing_slicing
  - https://rust-lang.github.io/rust-clippy/master/#string_slice