what I do to catch a rodent..first i know that they almost always run along walls and end up in lovely dark places like closests..if your basement stairs are open stairs, make sure you shove a towel or block the crack under the door because they try to climb down the stairs and fall on to the floor..that's bad...next i turn off everything that makes a sound and watch the dog..he hears better than all of us and will usually point the way. turning off the lights and sitting quietly in the room until they forget your there will get them started exploring....if that doesn't work you can either get live traps from the hardware store or you can get creative on your own..staircasing books up to a short bucket with yummy honey type grain down in it will get them to climb up lean over and drop in...then they can't get out of the bucket..or you can set a trail of grain if the dog will leave it alone to a food source and catch them that way . Check all laundry and for god's sake dont' put anything in the washer or the dryer without looking first..check your water sources where condensation could build up and provide a drink. Closests are the best bet. I have a story about a mouse if i can ever get the time I want to illustrate..i think i put one in the art section..if I didn't, i will tonight. We had an artful dodger that taught me everything I ever needed to know about finding a mouse in a house also check the back of dishwashers and washing machines..we had a three legged hamster move about 20 lbs of dog food in to the back of one before we found his hideout..he had other interesting things in there and one night I saw him dragging the hairbrush across the floor towards his new home..that is how i discovered where he was.. we had actually turned him loose to lead us to his lady friend that had escaped the week before..both led a long and happy life safely back in their tank after that. I sure hope you find him! Good luck