How do I reset layer info after running a routine?

[RJW]

I've written a simple LSP routine that changes to the DIM layer then starts
Autocad's dimension routine. How can I make this routine change back to
whatever the layer was prior to running?
For instance, if I was drawing on the Wall layer and I ran my dimension
routine, I'd like it to automacially switch back to the WALL layer rather
than staying on the DIM layer.