Have a look at the attached images. We use side nets as that allows us to continue to manage the canopy, even after the nets are on. Many vineyards use over-row nets but, while easier and less time consuming to apply, these don't permit any further trimming after they in place. The downside with side nets is that there is a lot more clipping of the nets together to keep the birds out. We buy the bio-degradable clips we use in lots of 500,000, so think about that too!
It took 2 guys working flat out nearly two weeks to finish the clipping, then last weekend a gale (150km+ winds), broke quite a few clips so we had to replace them. In fact the winds were so strong on our 'Highfold Block' that several vineyard posts snapped off - now that's a strong wind. These are not thin sticks we are talking about. We like the sloping vineyards for their extra sunlight hours, no frosts and the great drainage, but times like this do make one realise the saying "no gain without pain" is very true.
Why do we need nets? It's because of the *$%%$@!# birds! If we did not net we would risk losing upwards of 20% of our fruit to the little devils. If they just took the odd grape and flew away, that would not be so bad, but what actually happens is that they peck a hole in one grape on a bunch, enjoy some of the juice and move on. That grape then weeps the rest of it's juice onto the bunch, it then goes mouldy and is lost to us. On top of the nets, we use measures like scarers and hawks (we hang meat out for them & when they come for the meat, they frighten off the smaller birds). Other wineries use all sorts of things: electronic scarers, scarecrows, gas cannons and so on. It's a real battle and people try all sorts of things, but believe me, the birds work out ways around all of them. They may be small, but it's not a one-sided fight!!!