You have been transfering to secondary too early. Always wait AT LEAST a couple days after fermentation is over before you rack to secondary.
Secondary Fermentor is a misnomer, it is the clearing or bight tank, and is not a necessary step in making good beer. It is used in commercial breweries to clear up space in the main fermeter to make as much beer as possible. Unless you need the space, there isn't usally a reason to even transfer to a bright tank.
If you do decide to transfer to the bright tank, then there is usually enough CO2 in solution to be roused out and creat a "CO2 blanket" on top of the beer to protect it from oxygenation. As long as you are careful not to splash or rouse the beer to much while transfering, you shouldn't have a problem.