Placing your Mastiff in a kennel is a great idea if you are going outside of your home for any time period.
I know that I place mine inside of his kennel when I am leaving my home for a shopping trip and I have to make sure I give him something to keep him occupied while I am gone.
I know this can be a challenge, but if I forget to do this he will start to chew on his area and try to get out which he has done with a couple of them only to greet me at the door when I get home.
Here are some things that you can do that I have found to help prevent my Mastiff from chewing up his kennel.
The first thing that I found that helps out tremendously is to give him a bone before I leave him alone.
I know that this is a fairly obvious thing to give them, but you will want to find one that will keep him occupied for some time in case you are going to be gone for any extended period of time.
So I would have to say you will want to get a big thick strong sturdy bone and not a rawhide because if yours is anything like mine he will have the rawhide gone before you even leave the room.
The second thing that works to help in getting them to calm down and keep your Mastiff from chewing up their kennel is to have some nice relaxing classical music playing in the background for them.
I know that when I forget to put the music on for mine he generally will be barking and doing the loud howling noise that every owner has probably heard before.
However, when I do put the music on he generally will lay down and chew on his bone for the entire time that I am gone in between naps.