Lambie said..
When heading out to sea with no landmakrs to aim for - you need to use your angle to the waves as your 'directional' guide - be aware that often the wave direction isnt quite perpendicular to the wind but it will give you the best guide.
Also remember that the wave direction will wrap around land, so to get a good feel of the prevailing wave direction you will need to be a fair bit out past the breakers. If you are near a point, wave direction can change quite a lot.
To get a good read on what angle to go over the waves, try stopping once you are in clean water and putting the kite to the edge of the window in direction of travel. Take that angle to the waves as a broad reach (going downwind slightly by about 15 degrees). Add about 45 degrees to that angle and that should give you an upwind direction of travel that is achievable (with a well powered kite). Head off in that direction and note the angle to the waves.
In time you'll get to know the feel of the kite when travelling at maximum upwind capacity. Trust that feeling more than sight markers and you'll find making upwind going out to be almost as easy as coming back in. It takes a lot of practice though, so keep honing the skill by trying to always go more upwind than your sight marker and feel if the kite is going to sustain you at the new direction. If achievable for more than 5 seconds, change your sight marker to the new direction of travel and start again. Remember the sight marker is subservient to the feel of the kite's ability to go upwind, not the other way around.