If you have the gear required, consider this method:
https://www.youtube.com/watch?v=1qIP6HuCwaI
I actually got 10 per hour (but I've invested 15 points into luck, so theres that) I got my first 15 shackles through mound maker but I just got bored of 3v1's, as others have said, once you nuke the host, you've won, but it still takes way, way more effort than just farming those 2 dumb ass skeletons.
From has really done a number on the convenant rewards this time round, and mound maker might have the worst rewards of the lot. The pyromancy spell, warmth, while cool in concept heals very little, you could argue that it would be great if you got hit with an Undead Hunter charm, but warmth doesn't do anything an equivalent 25 faith miracle can't, it might have some arguable usage if it used int rather than fth...
and the rank 2 katana has some of the worst base dmg of any katana in the game, even if it has good scaling. I'd nearly rather the covenant rewards were purely cosmetic and were just for show, and it least it would be more honest than the bargain basement junk they give you for all your hard effort.