We travel light and aren’t inclined to carry anything heavy if we don’t have to - so kryptonite locks are out.  We travel with a cable lock long enough to wrap through both bikes and around a post, but mostly we rely on common sense.  We almost never leave the bikes unattended, they’re in sight but locked together when we stop for a meal, and if we stop to see a site along the way we take turns.  

In 35 years of bike traveling, we’ve had two bikes stolen - both at home.  Cities are the worst.

For my most recent tours I’ve been using one of the titanium U-bolt locks.

Sure it’s an expensive lock (mostly because the $USD is high against our $AUD ) but the lock is cheap, lightweight insurance. 

On every tour, I’ve found there is at least one or two situations where a good lock is essential. 

https://tigrlock.com/collections/tigr

With you there, Graham -- I have a couple of these, including the more recent "wide" variety.  On tour, I use that with a Kryptonite cable.

But:  A couple of years back, I gave our daughter a really nice red 1980s Sekine bike, together with a TiGR lock. (I'd bought the bike from the bike-recycling group of which I'm a member. Cost all of $200, but it looked the bizness.)  It lasted just a couple of days:  she parked it on a street in downtown Hamilton (Ont.) where she lives, locked it to a post, and thieves cut the TiGR with an angle grinder. 

She still has & uses the "elder sister" to the red Sekine, a slightly scruffy but defiantly reliable blue 'un, which I bought for my wife in 1978.  That has a Kryptonite lock...

Cheers,  John

John that answers my question about what’d I need to do if I lost both keys to my Ti lock and it was holding my bike to a rail at the back of a country pub. :)

Even if battery powered angle grinders disappeared, the LockPicking Lawyer will pretty much always post a video defeating any affordable/carriable lock I've ever looked at! 

I have an Ottolock I've used on many solo tours but I'm now more worried about me not being able to get it unlocked than a thief seeing the LockPicking Lawyer video cutting through it with a butter knife.  Maybe the newer ones are better - this one hasn't aged well.

I've got back to carrying a hardened (takes at least a steak knife to cut through...) cable and decent Master lock and minimizing, if not completely avoiding, any outdoor overnight storage.  The cable is easy to pack and I've always used it when biking with my wife on day trips/shorter tours.

Y'know, Graham, if you bought a second lock, the folks at TiGR will give you a second set of keys which are identical to your first set.  When I bought my spiffy new red/wide lock a few years ago, they sent along a card with my key code on it.  I now have four identical keys for my two locks.

Of course, the old swings-and-roundabouts dilemma arises:  I have trouble keeping track of twice as many keys as I use to have...

John good suggestion, and I did buy two identically keyed Ti U locks for when my wife and I ride together.  

Being able to ‘daisy chain’ the two U locks is a bonus, especially when we use our Bike Fridays. I’ve found that mono tube bikes, like our BFs are awkward to lock compared to diamond frame bikes.

Graham, that is also my perception of the short but strong titanium band locks. I look at my monotube recumbent and a typical 15x15 cm square post that I frequently use to lock my bike, and even the "long" model is too short. My much longer coiled cable lock is also too short to go around larger bricked posts.

I think Wayne Estes offered good advice, and it's mostly what I do.  I'll add the following;

1. you can buy brake bands from Adventure Cycling that will lock your front and rear brakes (similar to the velcro straps Wayne recommended).  I always do this when I leave the bike for a quick run into a store.  An unaware thief will be surprised that the bike won't roll forward easily, or maybe not at all, and abandon the attempt at theft.  
2. even if you do nothing else, always take your wallet and cell phone with you when you leave the bike.  As long as you have your credit cards and a cell phone you can survive while planning your next move if the bike gest stolen.  
3. I have no concerns when leaving my bike outside a small town store or cafe.  But in a larger city I lock it up.  
4. I only carry a cable lock.  It could be cut with a bolt cutter very quickly by an organized and prepared thief, but the act of doing so might alert others that a crime was underway.  Just the fact that the bike is locked up might be enough to discourage a "crime of opportunity" thief and cause him to look for an easier target. 
5. I've ridden coast-to-coast twice now, and done a couple of other 1,000+ mile tours as well.  No one has attempted to steal my bike.  However, I am careful with how/where I leave it, especially so in the large cities.  Avoid the larger cities and you will avoid most of the crime.  
6. Carry at least 30 feet of strong nylon cord with you - it will come in handy for campground use as a clothesline and such.  And if you catch someone in the act of attempting to steal your bike, tie them up and then hang them by the neck until they die.  They used to hang horse thieves in the old west days, and anyone stealing a loaded touring bike deserves the same fate.

George as per a previous Forum thread, I’ve also fitted an AirTag to my touring bike (s). At least I’ll know where it’s been stolen to. Even if the cops won’t be interested in retrieving it.

The most likely use of the AirTag though is to remind where I left my bike. Especially in large cities. I also have an AirTag on the titanium U bolt key. The scenario of my losing the key and having to find an angle grinder to liberate my bike, is more likely than a bike thief taking off with my very non-flashy looking Thorn Sherpa.

I do carry some nylon cord. I haven’t used it yet for lynching bike thieves, but I did use it as a dog lead to save a stray dog from meeting an early demise on a busy road.