[is_taken]

Other code quality issue encountered on a quick review:

  - use of utils package
  - use of models package
  - naming of receivers (too long)
  - returning empty structs instead of (nil) pointers
  - too much log.Fatal scattered around the code
  - unhandled errors, inconsistent error handling
    sometimes handled twice a la log.Printf(..., err) then    return err
    consider error wrapping here
  - useless use of err2 variables
  - use of Must functions which will panic if fail, transition to err producing fns
  - stuttering (digger.DiggerConfig)
  - naming things ...Impl instead of naming the interface ...er || ..or
    This is done correctly in tf.go, not so good in locking.go

For a complete review i would need more time.