I used tape. Ann can attest I was a mess with glue. Plus with more than 1, glue didn't seem to last long. Brodie ended up with a bald patch on his head. The glue got ripped out when he was playing with Kooper, our doxie who was alive then.
Not that I am a pro, both my dogs have 1 wonky ear. Deacon has really, really thick ear leather - his were tough. One had a mind of its own. He looked so cute when his ears were taped, but we love him with his prick and partially prick ears. I did a year, not that it did much good, lol. I thought I read you want to at least do it until their adult teeth come in.