While this is not possible in all cases, you have only one option when you see a dog approach: YELL.
Call out to the owner. Call out to the dog. Make it verbally clear to anyone who can hear that the dog needs to leave the kite alone. Yelling 'Go away!' or 'No!' or 'Is your dog going to eat my kite?' all might appear as over reactions to the owners or to bystanders. But if it saves your kite or raises the owners' awareness of what's at stake, we win a little.
Two things are more likely to happen if you yell. 1.) If the dog comes to you or runs away, you win. 2.) If the owner thinks YOU are scared of the dog, they are more likely to attempt to call back their dog.
That being said, and being a dog owner myself, for every responsible dog owner...you'll find 10 who are barely functional socially.
The bottom line for me is destruction of property is destruction of property. The only time this has happened to me, I chased the owner and demanded action. It's not a toy, it's personal property. If the dog jumped up, bit your iPod, and broke it, they would owe you compensation. Dog owners need to understand that this is no different. It should be framed as such from the moment you address the owner. 'Your dog has destroyed personal property of mine worth 200 euros. What are you going to do about it?'
Good on you for photographing them. That's not nearly as invasive as their dog f#%&ing up your evening.
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return." L daVinci