Dear Chris,
Even though many people think the Monarch caterpillars have toxins that keep them safe, there are predators to be aware of.  There are two ways you can protect the caterpillars.  The first way is to leave them in place and minimize the threats from predators.  The first reference below describes 13 different predators and suggest protections against each one.  For example, you might use netting over the milkweed plants to protect them from birds and some insects.  The second approach is more labor intensive and that is to remove the caterpillars and raise them in jars. If you do this you will need to consistently supply milkweed for them.  The same reference describes the process of raising the butterflies yourself.  Monarch butterflies need our help and thank you for being willing to do that.

https://monarchbutterflygarden.net/stop-monarch-predators/