So this is a repost from the other thread-thats-not-a-thread (Ask your OP :))
1st of all: He cannot actually detect evil auras of creatures of 4 HD or less.
2ndly: there is the spell Undetectable Alignment and the item Ring of Mind Shielding
3rdly: Just because someone rings as evil, does not mean it is killing material. There are cities that are governed by lawful-evil people, starting to slaughtering people just because they are ringing evil is generally an evil act just be itself. What a LG PC would do is trying to change his aligment, make sure you remind this at your paladin.
However, for the times that you want to keep the evil identity a surprise, there are spells and items that let you keep your aligmnet secret.
And then I wrote- Not sure where you get the '1st of all' rule- and I might be wrong, but I think paladins in Pathfinder have no HD restrictions on the ability. That said, the rest, OP, is gold. Use your resources to confound the paladin.
Is the paladin using detect evil in civilized lands and just chopping the poor evil sods down?
Many civilized lands consider that Murder, a punishable offense, entitlement or not.
To answer your question, maybe use some CN baddies. CN is almost-Evil; it's about as close to evil one can get without poking the hive.
--Please note this post makes no effort to reconcile the OPs original gaffe of dual posts, nor does it make judgement on the snafu. But if the Pally is wonking your game, CN enemies do confound detect evil attempts.