I don't know what game you're playing, but we're having a very different experience. I'm on my 34th day and I still haven't found the most basic of schematics - no crossbow, no sledgehammer, and no spiked club. Though, I have found ten or so rocket-launcher schematics, countless AK-47, and a slew of others ALL that I already have. I died just recently as a feral spawned right beside me as I was repairing equipment in my menu. It literally killed me in two hits while wearing full armor. The first hit stunned me so by the time I was swinging and backing away I was already dead. Since I play single player there's no one to watch my back. How can you predict a zombie spawning under your feet, right after you just cleared the whole building? And on the way back, attacked by six zombie dogs (luckily survived that). Yea, I'm going with not the same experience.
I get what you're saying, it is definitely easier with two people. But I've also done it in single player and have the achievements for it. Dogs are easy, you can outrun them. It's wolves that are the bother. Build a makeshift tower and snipe them with a bow, or run and jump into the water. They slow down much more than you do in the water. Same with bears, but they take a bazillion hits to kill on insane. I've been three hit by a lumberjack in full iron armour, all around the 500 mark a few months ago. (Which was totally my fault, stopped in the middle of the road to answer my phone). But that was back when my wellness was only around 120. Now, 0 deaths routinely, in several games. This is all at day 90+ on insane.
You just have to be smart about it. They suck at elevation, build a railing system above them and shoot through. I've built an impenetrable base on single player-insane with an electric fence all the way around, towers, spotlights, spikes you name it. I have pictures of it all, if you think about it you can get by without dying pretty easily once you're used to it. Master elevation and you've beaten every creature in the game.
To answer your indirect question, you can't predict zombies spawning at your feet. But you can stop it ever being a threat. Don't stop on ground level to repair things or go into your menus. Build a little tower in the street, stand on it and voila. 100% safe.
Mind you, I have around 600-700 hours played. Not sure how long you've been at it!
Schematics can be a female dog I agree. So can gun parts, I've found like a thousand pistols, two AK's, a rocket launcher, sniper and an SMG. But, I'm consistently ALWAYS missing one part of a magnum, which makes me cry.