In my opinion, you're already doing plenty. I don't use the eartags and most likely never will. Most of this fly control stuff is made to take money out of your pocket, not put it in there.
Sometimes I keep a rub out that calves can use, but the cows are pretty much on their own. If they've got face flies or horn flies they can't reach with their tail, they need to find a buddy.
If you feel like you need to do more, get one black cow that comes to cake. That's why God put black cows in Texas - to save on fly spray. When all the flies in the country pass up the red cows and get on your black one, all you have to do is cake her up and spray her. :wink: