Due to the discomfort large mammals like humans experience from thorny plants, the numbers of such plants incorporated into gardens have declined. This is particularly the case around suburbia where there is less remnant bushland and general growing space.
There are a number of thorny fruiting plants out there and in addition to their excellent produce, the thorns themselves can be used to advantage in a number of ways. Best not to locate them adjacent to a thoroughfare where they’re most likely to interfere with passers by, but to use their inherent qualities for other garden functions. Ie; Habitat/natural pest control, security, food and tools.
In the wild, many small birds rely on the protection of thorny natives to raise their young and rest at night. Being petite, there are many predators to deal with and this protection is sorely needed. The importance of maintaining this habitat is even greater in suburbia due to the large populations of roaming cats. Small birds are generally insectivorous and provide a huge benefit in the way of natural pest control.
If you’re sick of drunk people jumping your fence to sleep the night on your verandah or if you just want to bolster security around your house. Criminals hate getting spiked like the rest of us so some raspberries beneath an insecure window, for example, can be a cheap and efficient way to dissuade unwanted entry. I have effectively used a native Raspberry (Rubus moluccans) to create a productive security barrier between houses where previously the occasional fleeing miscreant would make their escape!
Some cacti spines have been used historically as sewing needles through Central and Southern America. Golden Barrel Cacti are a good species for this as the needles are large and curved, particularly at adulthood.
Some of the most interesting possibilities including a few native bushfood species; Natal Plum, Finger Limes, Bush Lemon (and other Citrus wild-types), Berry Brambles (ie; Raspberries, Blackberries, Loganberries, Boysenberries etc.), Cockspur Thorn, Tree Violet, Rose-hip Roses. There are also some useful local wattles that are quite prickly and can be incorporated in secuity plantings as nitrogen-fixing nurse trees/shrubs.