I need to buy a new, durable laptop. I want it to be the last laptop I have to buy in the next ten years?

If you do that then for the last 5 years it will be hopelessly obsolete.

10 years? That is asking a lot. Far more than is reasonable. A laptop from 2004 couldn't hope to keep up with the workload of a current generation machine. If it is up to the tasks you have for it over the next 5-6 years you are doing pretty good.

Lenovo is the number one rated Windows laptop mfg, followed, in order, by Asus, HP, Dell, and Samsung.
At the bottom of the list, from the bottom up, you have Sony, Acer/Gateway, and Toshiba.
Every mfg has some lemons and every mfg has some true standouts. Much depends, however, on the way in which you are going to use the machine and for what purposes.

The Lenovo X240 appears to be a love/hate affair. Most of the negative reviews I saw were the result of expecting it to be something that it isn't or purchasing it without actually taking one for a test drive. Many complain of the way the touchpad works, the keyboard, or the trackpoint, all of which are user perspective issues. Many other users like the way those things are configured/work/made.

A very good alternative for you might be the Samsung ATIV Book 9 Plus. While PC Magazine reviews give the X240 a rating of 4 out of 5, the Samsung gets a rating of 4.5 out of 5. You should go and give each a test drive to see if you agree with some of the negative user reviews or if those user issues aren't issues for you. Obviously, do the same with the Samsung as well as some of the other competitors.

Those two machines are both UltraBooks which I expect is what you are after.
Historically, Lenovo Thinkpads are the creme' de la creme business laptops. As I'm never interested in gaming performance, my choice in laptops always has to do with durability for a mobile user, not for the casual home user who wants to go from bedroom to living room, to kitchen, etc. In that regard, the Lenovo Thinkpads and the HP EliteBooks and ProBooks are pretty much what I limit things too. I expect that there are some Dells in this league as well, but I have a long standing dislike of Dell going back a long ways for some of their design and business/marketing practices which I found downright offensive.