Most people will have the tank drilled in a back corner. You can buy prefab internal overflows although I don't know if you can get one the right size for a 10g. You could make it from acrylic and silicone it in...be warned that silicone doesn't stick to acrylic very well. In a tank that size, you might cut a piece of 3-4" PVC
longways so that it fit from corner to corner. Then cut the weir in the top and silicone it in. Or...you can just use a standpipe. You'll need a screen around the standpipe intake though or (yeah, been there...done it already
) a snail or hermit will get in it and stop it up. This will result in a wet floor.