Even after a dog's ears are "up" they have control of them and can put them up when alert, and down when they are relaxed.
At 5 months old, Cooper is still in his crazy-ear period that coincides with teething. It's normal for them to go up and down. I'd say if they are mostly up, he's doing fine. It's only if one or both ears is consistently "down" that this is the age to think about glue or tape to help hold it up while the cartiledge is firming up, and he's growing into the ears.