Making your bike theft-resistant

Sometimes it's cheaper to buy a nice item and recoup a high percentage of the cost through a high resale value than it is to buy a crappy item (or several, if they won't last as long and so have to be replaced) and not be able to recoup anything, since it's worth basically nothing 2nd hand. I saw some calculations once which showed that it's ultimately cheaper to buy a BMW for about £25,000 than it is to buy a fairly anonymous Japanese saloon for about £15,000.

You want a brompton (assuming you've out grown out of islabikes) as they hold their value best out of any bike.

I know a couple of people who have made money by buying a brompton on their cycle to work scheme and selling the bike as soon as they own it at the end of the scheme.

It will also remove the need to lock the bike up outside.

But to the original question, the vast majority of theft is opportunism rather than people stealing shiney bikes, get three different locks (d-lock, chain and alarm) so a thief will need more than one type of tool to defeat them, and replace all the bolts with something like atomic22... Much more effective than security through obscurity.