I don't have Aussies, but I do have Collies.. and have experience with the ears on Collies that can go up and down and in all kinds of crazy directions, especially during teething.

At 5 months of age, the ears are probably staying, how they are now.. however if you wanted both ears a like, you could TRY to glue the prick aer down but its a long shot... just because of age.

Typically if you want correct ears, you will need to tape and/or glue the ears, starting at a young age - by about 3 months of age, before teething starts, but you need to do it correctly. Chewing gum in the ear to make weighted down (or any other kind of weight hanging in the ear) will more than likely strenghten the cartilage and make the ear stand prick. During teething, the ears (in Collies so I am sure Aussies as well) will go up and down and all over the place, so if you want correct ears, you need to keep them down properly during these months.

I had a friend of mine who had an Aussie she showed several years ago and they used a fabric glue (I use Tear Mender fabric glue in my dogs ears), and she glued the dogs ears down to the side of his head to keep them down correctly.

Obviously Aussie ear sets are different that Collies, and I start my Collie ear training around 12 wks of age, and use tape (Elastikon bandage tape, with skin bond is best, IMO) to pull the ears up on top of their head correctly.. then use either tape or glue and fold the tips over to the inside of the ear.


Here is correctly taped Collie puppy ears

I've been trying to find a website that has instructions on taping Aussie ears down, but not having luck.... I know I have seen a site about it before, so I'll keep looking, if I find it I will post it here.