For those of you having trouble...
First of all, this is a pretty nice game. Its not the best defense game I've ever seen, but a lot of thought and time obviously went into its production and I appreciate that.
A lot of people were having trouble with "Level 10", and theres a pretty easy way of taking care of that. Im not sure if it works on any other difficulty level (probably not), but I pretty much blew through the game using about 2 to 3 "Rats" on each stage, they just killed everything. Once I came to level 10 I tried the same tactic, and all my rats were destroyed by a Cat and Owl. However, I found a way to defeat them.
If you send out an Owl in the beginning, he'll start killing the mice that come his way and eventually start attacking the Cat and Owl. He'll die, but right after he dies send out another Owl or Cat, depending on your cheese, and rinse and repeat this, until both the Cat and Owl are dead, and you can use your regular tactic on beating the game. It may not work on any other difficulty setting, but its worth a try.
Once again, great game, I'd love to see more.