I noticed that the possibility to find a safe location is not given every time.

It take a big amount of time to get a safe location.

Implementing a mode where only surface locations are generated would be a good.

I'll edit the message to fit it.

I'm not sure I understand, currently generating surface blocks is the only mode that is implemented. Other modes (like min/max-y or Nether mode) aren't supported yet.

I randomly was teleported into a cave. Could be that this was the highest block solid at that location, water came from above. Without the -f option the possibility of a successful location search is pretty low. So it has something to do with the can build check or the safe teleport location check.

Uh. yeah, it will teleport to the highest solid block so if everything else above your head would be non-solid then this could happen. I guess the ability to provide a minimum height (issue #1) would solve such issues too. Could probably set it to the sea level by default too.

I personally don't see any issues with the rate at which it finds locations though. I have it running on my server without issues so that might be due to your setup? (Like too many protections or not enough valid block types set in your config)