Extended run's fencing Q

I found a roll of old chain link fencing, it's about 4ft tall only. So I wanted to put up 2ft or 35in chicken wire on top of the chain link. So making it 6ft or 7ft tall. This stretch of fence is along the horse field and where the fox has been seen going by.
Can foxes jump 6 or 7ft? For the bottom, I was going to lay 2ft wide boards on the ground and 2ft up along the fence.
I still have to buy and put up the front fence so it's enclosed on all 4 sides. The back is the dog's yard, it has 5ft chain link and the other side is the chicken coop w/their fully enclosed run. I won't be covering this run w/wire like their full time run is. This one is for them while I'm out in the yard, but won't be outside all day until bedtime for the chickens.
I don't see them flying over, only the Japs and only if something goes for them. The others are too big or fat to fly high enough. The new area will be about 3 times larger than the 13x13ft dirt run. It also includes the area behind the coop up to the duck's pen. That's where the door will be for me to get in/out. The chickens will go in/out the human door of the coop.

 

I'm not worried about fly overs. That happens all the time with the mini section I added to the back of the coop. The Mulberry tree drops tons of berries and I let them out there to pick them up for me. A bird or two have gone over and I had to yell at the chickenkiller to stay away while I caught them and tossed them over. But the bigger area, they won't be contained so close to the dogs. The chain link I added is just too low, they all will fly over as soon as they realize it. That's why I have to add to the top. And I rather use stronger fence to start with, since eventually it will be a permanent run, just not this year.