I've feared for my sight many a time in the years of dragging C&S inside, nothing's scarier than a big agave, terminal spines extending like wicked fingernails!
The solution I've used for years is in fact finger nail trimmers!
They work great!
Don't be tempted to try using scissors or a knife!
That spine's hard as rock!
It does leave the plant permanently scarred, or declawed, but unharmed physically...
Aesthetically, though, the damage is real!
Given time they grow out of it, but these are slow growing plants, and with no other solution, the new spines are doomed come fall anyway...
The grand solution...WINE CORKS!
Simply slice them into appropriately sized chunks, and spear them onto the terminal spines!
You lucky folks in warmer climates may like to try this with larger specimens that are reaching into walkways too.
For most of us, though, we can split a cork into 8 or 10 pieces. Use a very sharp knife, and be careful because round objects are tricky to slice!
Don't press down too hard or the cork will just compress. Repeated slices are needed!
I prefer a very thin non-serrated blade.
Once you have the cork chunks, stick 'em on!
If your agave is small, or doesn't have thick robust spines, you may need to pinch the spine high up, to support it.
Otherwise, it's pretty darned easy!
I must admit, it does look a little funny...but when it's time to put the agave back out to soak up rays, and when you can keep your distance, just pop the corks right off!
If you don't generate your own cork supply...Ahem...it's likely you know someone who does, but if you still can't find them, you could buy them online or at craft stores.
An even better source may be local restaurants or bars that serve wine. Just ask whether they might have a few lying around, or even call ahead and ask them to save them for you!