It's always possible that property lines were lost or abandoned before you purchased the property - the first thing you need to do is check with your county assessor for a legal description of your parcel (most times the description is on your deed). You might also need to have a "civil engineer" to come to your land and make sure that the lines are marked correctly. Parcels are set in measurements from the main roads - by quarter miles and feet from the center of two other measurements. If after your property lines are confirmed and staked out - then if the pretender who tore down your fences is wrong - you can sue him, for the cost of replacing your property line fences. There is another way that your property lines might change and that is if a utility company has placed an "offset" or "easement" for future need - Electrical, natural gas, and broadcast lines have precedence and may arbitrarily take some of your property for their use. That is called "eminent domain" - and all counties, city's and municipalities reserve the right to do that for the public good (uses include roads and railways - channels for water, etc)
All this you can investigate on your own - you have time if not money.
Under California law, length is not an issue for carrying knives in public. The length of the knife is irrelevant unless its a switchblade. In that case, it is illegal to carry if it is longer than 2.5 inches (PC 653k)
The only thing that matters under California law (PC 12020(c)(24)) is whether or not it has "ready use as a stabbing weapon. What this means is, if you have a folding blade of any length, you can carry it concealed. If it is an open blade, no matter how large, you can carry it, but it must be exposed. You could literally walk down the street in California with a machete or broadsword as long as it carried exposed (not brandished)*. Likewise, you can carry a foot long blade in your pants* as long as it folded. So the knife you have with the clip can be carried either completely concealed in your pocket or exposed.
When it comes to carrying on k-12 school property, the blade cannot be longer than 2.5 inches (PC 626.10) but schools generally prohibit them by rules anyway.
It is true that Los Angeles has stricter laws on the books regarding knives but they are probably not enforceable because of the preemption of state law.
There is nothing in the law that prohibits a juvenile from carrying a knife. The knife in the pictures are completely for you legal to carry in public.
*EDITED IN RESPONSE TO JOHN S.: Wow, he sure is a defense attorney! OK, its true it doesn't legally have to be "in a scabbard." But I don't see any other reasonable way to carry a knife (or sword). In one's hand? Then they face the possibility of 417 PC, Brandishing. So, yes, I do concede that the law does not require a scabbard and I actually (still) appreciate the hairsplitting.
It was only dictum in my answer but I need to do some more research on case law on the concealed carry issue in a backpack. I suppose if gun laws are any guide, it would depend on if the back pack had a lock on it or not.