Secrets in Paladin are an interesting topic. The concept of Secrets fits so well it something like Hunter (traps!), Mages (magic counters/tricks!), and even Rogue (surprising you is basically their main shtick). But in Paladin, the flavor is harder to find. Paladins are so open and non-secretive and fair and just. And additionally, 1 Mana is a touchy balance point; gotta bridge the gap between feeling like too minor of an effect to even be bothered by, and feeling unfair for only 1 Mana.
So yeah, as a designer, they definitely are the hardest Secret for me to design. But, despite all those challenges, we still keep finding cool new Paladin Secrets, and ways that we want to use them. I don’t want to be too much of a tease, but I will say that one of my favorite cards currently planned for the next expansion happens to be a Paladin Secret. ;)