Posted: 08/05/2016 at 16:25
The two I mentioned initially are spikey - hence the reason for suggesting them thorpeedo. They're often recommended as burglar deterrents. Blackthorn is the same but isn't evergreen. The only problem is that if you don't have something to plant into all the way along, it makes it tricky. You'd need to construct a raised bed of some kind to give a decent volume of soil to plant into. They won't thrive in pots or containers very well.
Sorry to disagree ppauper, but a rambling rose - not an ordinary climbing one - would cover that distance no problem once established. They don't require pruning either.You'd have to do a bit of research as some are thornless, but Kiftsgate is very rampant and jaggy and might actually be far too rampant for the size of space. An ordinary climber needs pruned to allow it to give of it's best because the flowers appear on new growth, so that may be a better choice in terms of size, but the pruning may cause an issue in spring. Whatever you choose, it would need a support for it to grow over the gate. Two posts and a top bar to make a little archway would do the job. Personally, I think that's a bit too much effort for you if you don't have a lot of experience. I'd go with Pyracantha and Berberis.
It might be worth starting a new thread if you decide on a rose. There are loads of people here who will be able to suggest something of a suitable size for your space which will give you the best result.