Labs ears

[Crawdaddct]

I have a year and a half old lab. I grew up around them, but this is my first one. Great dog. Training is going well. However, every time I take him out to the marsh to work, he ends up with a ear infection in his left ear. It seems to get worse every time. It seems like the vet is just taking my money every time I go in the door. Does anyone have any recomendations for ways to avoid this? Last time out I washed him as soon as I got home, cleaned his ear, and flushed with some stuff I found at pet smart. Two days later, he is walking around head sideways. Any help would be appriciated.