How to block off my crawlspace?

Hi all,
Hoping some of you may have some good ideas from blocking off my crawlspace ...We moved and I just realized that my boys are using the gravel lining my basement crawlspace as their litterbox!

I know how enticing it must seem to them...one big litterbox !! But obviously this does not work for us...

The area they are accessing is about 10 feet across by 2 ft high and I was thinking of using styrofoam and then putting chicken wire in front of this (so they don't just rip through the styrofoam...

I rent so I can't just go in and cement it over. Does anyone have any ideas for blocking this off? I have tried re-directing them back to their litterboxes but no go....

Thanks for any ideas!!!

How about big empty cardboard boxes from the grocery, with something inside to weight them so they don't get pushed around. Just make sure they're sealed so no one gets trapped.

If you have a Lowes or Home Depot near you, you can get them to cut a piece of particle board or something similar to a little larger than the dimensions of the "hole" and just prop it up against the hole.

Thanks for the suggestions!
I think they may scratch through cardboard. That's why I was unsure about the styrofoam too...but maybe the particle board would be ideal??

I'd be careful about 'just propping' it because they could get in behind it and knock it down on each other.

For any dangers spots, holes, fans built into the walls (with blades accessible to kitty), I've always used chicken wire and had luck with it. Just make sure there are no sharp edges.

Thanks again all! I am going to get on this project tomorrow and get some particle board? (I will make sure its fastened securely, Larke..Thanks )..and some chicken wire in front of that. I have heard they hate it on their paws so hopefully will not try hard to get into it...

I use wire shelving grids (the ones that make modular shelves) to block off areas from animals, build rabbit cages, hay racks, etc...

They're very sturdy. You can screw an eyehook into a wall and use a ziptie to attach a panel of grids, and it'll stay. That's how my rabbits' pens are anchored. You can get a box of 17 grids at Target, Shopko, Bed, Bath, and Beyond, etc. for about $15. I find them on sale for $10 a lot.

We made a little wooden railing for our crawlspace. It's not that little, but it counts, and it usually keeps Gemma (and Tiggy and Chloe, once) out.