Hi there
I've been having a terrible smell come up from behind my washing machine. My first thought was something was wrong with the plumbing and through investigation I've realized that something has been living above the insulation directly below the washer.(we live in a mini-home) The insulation has been pulled out and smelled awful and had droppings all over it. Im not sure what animal it is... perhaps a squirrel or a rat... anyway my question is if there is anything I can put up above the new insulation to deter any animals from returning?? Thanks.

My favorite is Moth Balls. I use moth balls for almost any varmint I do not want to return.

Try to find out HOW they got there and eliminate that entry. Or,.
They'll be back". :)

You may have mice. If you have a squirrel or rat you would hear them in the walls. They are not small animals.
Like Shunned said, find out where they are coming in. Look around the piping at the floor or the dryer vent where it exits the house. Mice need only an opening the size of a dime to enter.

If you can replace the insulation, do it. It will not prevent any more animals but it will help with the smell/health hazard and R value of your wall.