Great question — answering as the UphillTech team:
In general, the "anti-vandal" or "anti-theft" refers to the goal frames themselves, rather than the nets; there's very little you can do if someone is actually out to vandalise the net with a big pair of scissors or equivalent. The simplest solution by far is just to put the nets up when you need them - this then just becomes a question of whether it is more cost effective to replace the nets when they are stolen or have your staff time spent putting up and taking down the nets every time they are needed.
Full answer by Philip Kendall: https://sports.stackexchange.com/a/15837 (CC BY-SA 3.0).
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