Pets and rules

I would like to indroduce a limitation on how many pets you can have standing at a time. To do this, there would be a (max pet standing) rule. It would be 15. Each animal that can be tamed will have a certain value.

Example: dogs would take up 3 space, meaning you could only have 5 wolves standing at a time. This would add balance and would make it so you can't just destroy every mob you see with an army of wolves. Mojang can add more to this but that is just my idea on the rules of pets.