It is an issue. The safer you make your run the more it can cost. Different materials have different pro and cons. To me there are a lot of trade-offs. The smaller the holes the more critters it can keep out, provided you don't have weaknesses at doors or windows. How the material is attached makes a difference, either leaving gaps or letting a larger predator get a grip so it can pull it loose or tear it. Heavier material typically has larger holes which can let small critters in. The weight of the material and the size of the holes both affect cost.
Unless you have dig protection some critters can dig under. Heck some critters can just force their way under wire with just a tiny opening between the fence and the ground. Many critters can climb or jump really well.
Practically any predator can hunt during the day, even the ones that are considered mostly nocturnal. I've seen bobcat, fox, coyote, raccoon, skunk, and even possum out during the day. That possum surprised me. 1:00 o'clock on a bright sunny day it was going through my compost pile. Still, your biggest risk is at night. Human activity tends to scare them away during daylight, though some people have reported a fox grabbing a chicken within 15 feet of the person.
My biggest problem has been dogs abandoned in the country. Daytime attacks. That's why I stopped free-ranging and started locking them up during the daytime. I use a philosophy of a predator-resistant run for the daytime and lock them in a predator-proof coop at night. My main run has 2" x 4" welded wire sides with an apron for digging critters. About 2/3 of it has a solid roof but the rest has about 7' high sides and netting over it. The netting was to stop a turkey form flying out, not to keep predators out but it does stop hawks. Those sides are going to stop even really large dogs. I's possible a raccoon could climb the fence or come across the coop and come down through the netting but they never have.
Then I added an area surrounded by electric netting. This gave me an area abut 45' x 65' that they can roam in really well protected from ground based predators. It does not protect against flying predators but in six years with it I've only lost two to flying predators, a hawk and an owl.
I don't know what the right answer for you is. Part of that depends on how precious each chicken s to you. How heart-broken would you be if even one was lost? Or just how risk-adverse are you. Good luck on your decision.
This is a very well thought out response. I am of a similar mind. The coop/houses are as secure as they can be and the birds get locked in them overnight when the most predators are the most active. The runs I have are secure, but not as secure as the coops, and will stop my primary daytime predator, coyotes, with 2"x4" welded wire, as well as prevent access by hawks from above. Think about your predators, day and night, and build for them. Also know that if you do not have the funds to do things the way you want immediately, you can make modifications later. While this may not be the most secure route, it allows time for you to save up some more cash. My coops/runs are far more secure now than they were a few years ago. For example my skirt got added about 6 months after the initial run was built.
How do you get a 10x30 run out of two 10x10 dog runs?
You have eight 10 ft. panels total from two 10ftx10ft square runs, you take two of them off the ends of one kennel and add them on the other to lengthen it. So you have two sides that are 3 panels each (30 ft) and two sides of the run that are 10 ft each (still eight 10 ft panels total).