Is It Too Much to Ask for Decent, Respectful People in This World?

Imagine: you are walking down a dead end. You come to a sign that says "No Tresspassing. Access area one block down" that is hung nicely on a fence, in the same area where you thought you were going to walk. Near that sign there is another; it reads, "Beware of dog". You hear a growl, and hear that dog. The very large dog starts to bark, enraged that you have come near his territory. What do you do? Do you jump the fence?
I hope you wouldn't jump the fence.
I am a mama bear, and I am on the rampage.
My family and I were eating a peaceful meal (tee hee..'peaceful') when our dog outside started to bark loudly and fiercely, more so than ever. Curious, I look out our kitchen window that faces the private property next to our fence. Nothing. Hmm, it must have been a squirrel.
Then I see the movement. A man was in our yard, getting ready to go over our fence into the private property (To do that, he had to bypass a city-placed fence which was locked years ago by an unknown person). The dog is going mad, but behind his kennel fencing he seems like he is not a threat (we built him a safe kennel fenced-in area due to other delinquents who have jumped into the yard and threatened our dog with a box cutter.........). The man sees me in the window, walks to the fence and jumps over any way. Then, he turns back, leans over the fence with the "No Trespassing. Access area one block down" sign, rips off the sign and throws it to the ground before proceeding to run away.
I am seething. First of all, it is not my private property. It is owned by the city or some other larger group who I cannot trace. The sign was there to protect my property, the same I share with my small children, dog and husband. Second, would you have not turned away, seeing that there was another entrance not even 20 yards away, in which you did not have to hop a fence??
What else can I do? I cannot contact the unknown owners, although I have tried. I cannot call the police again since the intruder is gone, and they'll just tell me the same thing: 'he did nothing wrong in accordance to the law'. I don't have the money right now to put up a taller fence, one that cannot be climbed.  I can secure the sign once more, but is it even doing any good?
You jumped into the wrong yard, buddy.
My husband tells me to calm down. Calm down?! There was an intruder in our yard. An unknown, disrespectful miscreant who could have taken three steps from where he was and easily broken into the house. He could have damaged our property. Heaven forbid he fell or hurt himself on our property and then had the nerve to sue us! What if he came on a day when my husband was not here, when I was home alone with the kids? What if I was outside alone with the kids? What if he had a weapon?
And he's not the only one. What about all of the others who have jumped the fence, for whom I have had to call the police because they were selling/doing drugs within our eyesight, for whom I had to call the police because they were drunkenly fighting at 4am.....
Ugh. I am not in love with this house anymore. I used to love it's old charm, the fact that we started our family here, the nice big backyard we had to play in...
It's time to move. My nerves cannot stand this anymore. To actually rip down the sign when I was watching....
Am I wrong?