Tanya, I'm so sorry Fritz is ill.
You might try the boiled hamburger and rice with him, a little at a time, and make sure he is drinking plenty of water. YOu don't want him to get dehydrated.

Since tomorrow is a holiday, it might not be a bad idea to at least call the vet, and find out specifically what you can give him if the problem starts again. That way you won't have to guess with the immodium.

It certainly could be the change in food, or just being in the kennel for a couple of days. But, better safe than sorry.

Hope little Fritz is feeling better soon.

Logan