I currently “lease” three domain names, two of which are (or were) in active use until very recently. That’s nothing compared to what I used to have (you might remember filesystems.org, plaintext.net, sysdot.com and pylogger.com). One by one, I let them expire after I didn’t make full use of them, or couldn’t renew for one reason or another.
The first big issue cropped up when I tried to renew zaidi.jp, the domain I thought I’d keep for a long time. Due to weird Japanese banking procedures, my transaction was declined and on top of that, the registrar suspended the domain for a whole month. By the time I could renew and reuse the domain, it was too late since I had already started relying more on my other domains and the need just wasn’t big enough to get someone in Japan to go through the renewal process.
This time, the DNS server I was using for all my domains suddenly stopped working. It wasn’t being looked after well so I should have expected it, but it had been running without problems for a very long time. This outage prompted me to find another DNS server or two, which I did, but another problem came up. I had no trouble updating the information for domains I had registered online, but the most important domain was through a local ISP and they still haven’t responded to my requests to update the info.
As of now, my blog and personal email is working, but the commercial domain remains unreachable. If only certain domain names could be registered for lifetime use and a more lasting solution found for problems which take this long to fix. That would bring up problems like trademark infringement or other forms of abuse, but workarounds can be found to avoid those. Maybe you could really own a domain (as opposed to “leasing” it) after using it actively for a certain number of years and if no one else contests its use.
Another advice I have is to keep at least two, geographically separate DNS servers that you can update (or have updated easily). I was doing this for a while, but in time, one server went offline and I didn’t bother to find an alternative until this one suddenly became unusable.