Always thought highly of Kevin Sheedy's life / football progression, in that it isn't always the naturally talented that make the best coaches but sometimes the not so naturally talented ones, who've had to work through the fundamental building blocks to hone their craft.
To replace Leppitsch, I'd be looking for one of these types who have worked to become a KPP, and have a good defensive sense.
Of those currently AFL coaching:
Adelaide - Darren Milburn
Carlton - John Barker
Collingwood - Ben Hart
Essendon - Sean Wellman
Geelong - Max Rooke
Giants - Stephen Silvagni
St Kilda - Danny Sexton, Dean Laidley
Sydney - John Blakey
Some state-based coaches:
Casey - Rohan Welsh
Port Melbourne - Gary Ayres
North Adelaide - Josh Francou
Norwood - Nathan Bassett
Port Adelaide - Ken McGregor
West Adelaide - Andy Collins (Still a big fan of his.)
Subiaco - Chris Waterman
Yes, some of the above aren't KPPs, but have been good defenders.
Others, to pull some names out of a hat, may include - Tom Harley, Nick Holland, Nigel Smart, Alistair Lynch, Martin Pike, Terry or Neil Daniher, Dean Wallis, Dustin Fletcher, Scott Lucas, Luke McPharlin, Corey McKernan, Wayne Carey (dare I say it), Warren Tredrea, Chad Cornes, Joel Bowden, Andrew Kellaway, Scott Turner, the Wakelins, Max Hughton, Darren Glass, Ash McIntosh, Glen Jakovich, Luke Darcy, Matt Croft, Steve Kretiuk.
I know I'm just pulling names out of a hat here.
A laughed when I saw Steven Baker, although a small defender, but you never know.