Ideas for building a new enclosure

I want to build a new enclosure for my dogs. Their current one is decent for the amount of time they spend in there, but I would rather a bigger one so I can actually add some different things for enrichment.

Their current enclosure is just a 10x20ft dog kennel... Massive tree roots keep them from being able to dig out, and thus far they haven't tried jumping or climbing out. They (and by they I mean Kirito and Mari... Rarity does not stay outdoors at all) are only in there while I'm not home. When I am home they are either outdoors or indoors with me.

I've put a lot of thought into different ways I could build their new enclosure. I want to get it out from under the trees a bit so I can have more open space to build different things for enrichment. Therefore, I will be adding dig guards.

I'm not sure which idea would be the most cost effective. I'm wanting to make it around 50ft by 50ft.

-One idea was just buying 6ft tall dog kennels and adding them together to make one very large enclosure. I would add rebar and cement to stabilize the fence; dig guards would be added to the bottom using buried welded wire fencing. Climbing guards would be added to the top (I probably wouldn't add this until later... since my current two have no interest in jumping or climbing out)
With this method I can use the kennel I already have and just add on.

-Another idea was buying actual fencing and nailing it to wooden posts 8 ft posts (2 feet in the ground, 6 ft above). The wooden posts would be cemented in the ground and I would also add dig guards like the above. Climbing guards if needed. With this idea I would do posts every 5 feet, and I would need 4 50 ft rolls of fencing or 2 100 ft. I was recommended to still add the top bar to the fence, so I'll buy that too.

Which would you recommend? Which sounds like the better option?

I've decided on treated wooden posts since they're cheaper and I can just nail the fence to the posts. I cant decide if I should go with 2x4x10 for $4 each or 4x4x10 for $12 each.

I'm also looking into different types of fencing besides chain link.