Best for me has been a 1/4-mile spool of 19-ga galvanized fence wire. You can also use short pieces like "twist ties", or longer pieces and "sew" the seams nice and tight.
I have a deer fence on t-posts around my whole property and the previous owners used zip ties to hold it together - I've had to replace many and in my experience ALL plastic zip ties eventually fail if exposed to the CA sun, even the black UV-stable ones in multiple brands. I tried out stainless zip ties and they do hold up - but they're expensive compared to a roll of fence wire, which is what I prefer the most.