First off, the laws were changed after that dumb Mariner case, BECAUSE of that case.
In Penal Code 653k, folders with a manual one-hand opening device (both holes and studs are mentioned) are declared 100% guaranteed legal.
Penal Code 12020 was later patched to declare folders that are carried folded "not readily available" and therefore OK to conceal. Nowhere in any of this or 653k is a length limit.
The real problem is that you cannot conceal a "readily avalable stabbing implement". Lengths aren't mentioned, neither is double versus single edge.
Now, the rules were written after a fatal stabbing with a wood chisel in SF. So I would NOT assume something with a chisel-like business end will slip by.
There's some reason to believe a "true sheepsfoot" could pass as a non-stabber. A "true sheepsfoot" has an unsharpened spine that rolls down to a straight edge and hits at a 90degree angle. For examples, see
http://www.myerchin.com - I'm very fond of the A500 as a plausible CA-legal concealable backup. In comparison, the Spydie Mariners don't drop the spine down to the blade at 90degrees and therefore could make better stabbers - but remember, as folders the Spydies are OK regardless, I'm just comparing tip structures.
Mad Dog once developed a weird critter called the "street razor" that had two sheepsfoot tips with a grip sticking up from the middle, an attempt to build a "combat sheepsfoot".
I think the sheepsfoot tip is the safest "legally concealed fixed blade" you can pull off. In the case of the Myerchin, the length is modest enough that you could probably avoid major hassles...try and conceal a 12" sheepsfoot and you'll get MAJOR trouble.
Jim March