If there is no natural space in the puzzle for the two arrows, you can just reformat the grid with an extra gap. I definitely like this arrow line idea.

Then this will be a very convenient and easy answer key. Definitely easier than counting double bridges.

Since this was just linked from the PR 2020 discussion: https://logicmastersindia.com/forum/forums/thread-view.asp?tid=2737#...

Just want to note one downside of this suggestion, compared to the version used on PR (which was to ask for a sequence of N numbers 0/1/2 counting the "horizontal" bridges in a row of N+1 clues). Namely, that the suggestion here has no fixed length. Some form of checksum like a fixed length or sum is very useful to avoid typos.