What to use to attach hutch & run?

I am going to make a run for my fosters and attach this to the hutch so they have free access - the hutch and seperate metal run were supplied by the rescue but I have to lift him in to the run at the moment. What does everyone use to secure the run to the hutch? I am planning to make the run 3 sided so the hutch will make up the fourth side, and have a removeable roof so we can get in there and interact with the bunnies. It definitely needs to be fox proof as we do get the odd fox wandering around here so I want to make sure they can't get in and the bunnies can't get out.

I was thinking something like the hasp and staple type fastenings - is there an alternative that would be better?

Carabiners or heavy duty dog lead clasps can be used to fasten the run to large eyelets on the hutch. If you need a bit more flexibility, you can add some keyring type split rings. Or double eyelets (one set on the run, one set on the hutch) and use the rods from the metal run?

Depending on the size of the hutch and the space you have, it is easier and more secure if the hutch is completely inside the run - like a mini aviary.

When our run was attached, we used cable ties (the big black plastic single-use ones), but it was attached to wire on the hutch end. It certainly wasn't massively secure. Carabiners come in different sizes so should work, or if you want it to be mostly permanent I'd 'sew' it together with copper wire or similar.

If you can thread them together, bicycle cable locks can be useful. There are some fairly thin ones and they come in a few different lengths. They don't have to be expensive ones.

I notice there are a couple of eyelets already screwed in on the left side of the hutch so I'm thinking maybe put a couple of eyelets on the run in line with them and use carabiners or padlocks to secure. Nothing on the right hand side but I could do the same there. As the hutch doesn't belong to me I will need to check if it's OK to add some form of fastenings, hope it would be OK as I'm trying to improve the set up for the bunnies Bicycle cable lock might be good for the roof if I can get them thin enough to feed through the mesh, easy enough to take off and on when we need.

I would love to have an aviary style run but I don't want to spend that much at the moment. This is my first foster bunny and I've already spent a bit on him so I'm trying to do my best within budget.