How to protect this foundation sill from elements, rodents?
An L or Z-shaped metal flashing is often used to bring water from behind a cladding out to the front of the wall (for example, when the upper part of a wall is clad with stucco/siding/etc and the lower part is clad with brick/stone/other masonry). Metal also makes a nice barrier against things that chew, burrow, and otherwise damage structures.

You could clear away the soil from the top of the foundation (probably a good idea anyway to keep insects at bay) and insert this kind of flashing. Ideally it would slip up behind the fibrous insulation layer and would project forward to the outside face of the siding. In this way the metal blocks access to both the furring strip gap and also the insulation. Secure it in such a way that critters can't pass between the foundation concrete and the metal, nor between the metal and the bottom edge of the siding.
Avoid applying a sealant between the bottom of the siding and the metal. Up to now any moisture that gets into the wall can freely drain out the bottom, but sealing this flashing to the siding would trap liquid inside the wall.
Alternatively, use a flashing that is perforated along the bottom edge so that liquid can drain out. This kind of drainage flashing is sometimes used at the lower edge of EIFS stucco installations. The one I've used was extruded plastic, though, so it wouldn't keep out rodents with sharp teeth so well as metal could.