After they finish teething you can usually tell whether the ears will be up or down. Sometimes if the dog has very big ears they are just too heavy it seems, but then again, our biggest girl in our last litter had very large ears, we figured she would be the one with floppy ears, and her ears went up first. She now looks like a cute little fox
If you really care one way or another (I personally don't, but a lot of people want pups with standing ears since it is standard), you can try shaving the ears, it helps get some weight off of them and assist the "standing up" process. Also, if that doesn't work, you can try taping them for a bit. And please don't go grab a roll of duct tape and just have a go at the poor pup. Ask a vet if you don't already know how to go about it. I was shocked when I was explaining this to a potential buyer once and they said they had duct taped one of their former pups ears completely together...they didn't get a pup
