How well does Trifoliate Orange (Poncirus trifoliata) do here in Vancouver, I don't think that I have ever noticed it. Considering it for a security barrier.
No reason to think it won't grow. Of course, you will have to wait for the planting to get big enough to do the job. And if there is a problem with determined trespassing anything recently planted will just get broken or stomped down. Unless protected by adequate fencing. And if you have to install a secure fence to protect the planting ...
There's a hedge of Poncirus trifoliata in a park in Orléans, I even took some fruit and sowed the seeds one year. Mine died but the one I gave to my sister was thriving before she removed it... because it had thorns ! ^_^ But if you consider it for a security barrier, it's a very good candidate. I tasted the fruit, they're no good, but maybe the zest in a "rhum arrangé" can replace kumquat... The hedge I mentioned is quite old and regularly trimmed, it survived the winter of 2011, where we all lost lots of maples, so I suppose that once they're established, they can survive low temperatures.
Trifoliate orange will do just fine in Vancouver. I do recommend they have good drainage especially for winter (mine is in a raised bed) and protection from cold winter winds (it won't kill them but it will damage any flower buds). But as Ron B. mentioned, it would take many and a long time to create a barrier - I got mine in 2010 and it is now about 1.5 m tall and just as wide. Trifoliate orange would make an impressive barrier as it does have long sharp thorns but there is also a cultivar called 'Flying Dragon' which has long curved thorns so anything going inside the plant will not easily come out (such as hands). I think the cost to put in a barrier of trifoliate would be rather high, but the plant itself makes for a great specimen plant - you get that wonderful orange blossom scent in the spring and in the fall the leaves turn to beautiful yellows, reds and oranges as well as the bonus of fuzzy orange fruit - which is smaller than a golf ball. The other name is bitter orange because the fruit is extremely bitter - neither the pulp nor the pith are edible - but they can be used for juice or jams/jellies if you like that sort of thing (I make a tasty jelly by adding some sweet mandarins).
