I sow first and net, but only about 6" off the ground. I use debris netting at this stage, well weighted down to keep the mice off.
Only when the peas are a few inches high do the supports and twine appear, the debris netting then moves on to be used elsewhere for brassicas and the like and it's replaced with any old netting sufficient to keep the pigeons off.
Then increase the levels of the twine until you get:
The darn pigeons have got worse over the years, I used to net my peas from sowing until about 6" high and then again when the pods were setting. After last year, I'm going to have to leave them on all the time.
This is last year's crop, totally covered after the pigeons had a go at them. They did manage to recover quite well.You can just make out the netting.