Recently, I acquired a few more knives than my narrow (and infamous) knife block could hold. One of them is a 10"chef's knive, which didn't fit in any of the slots of the existing block. I shopped a bit for a bigger block, but all those that held 10" blades were very big, and/or very expensive.
With children in the kitchen, I wasn't comfortable with installing a big knife magnet. (I'm also not thrilled with the aesthetics of these. I think they make a home kitchen look a little angry and dangerous.)
Jealous of my counter space, I wasn't enthusiastic about trading a perfectly good block and folding money for something bulkier, I managed to come up with something that works really well for me:
I used high intensity magnets glued (via hot glue gun) to the top of the existing block. These magnets each have a 12 lb. pulling capacity, so the knives are securely held to the wood.
For each knife, I put two magnets: one for where the base of the blade meets the handle, and another for the tip. Since I used the actual knives as a guide, the result is a custom fit.
These are my two most used knives, so it's convenient that they are the most accessible and easiest to put away.
I'm really pleased with this setup. It cost $4.50 in magnets (half of the $9 package), works very well, and takes up no extra counter space. (Since it's so hard for me to throw stuff away, not having a leftover knife block to discard is a psychological plus, too.)
By the way, while browsing around for knife blocks on-line, I came across a great idea on one of the forums for substituting the "laxative" mineral oil from the supermarket for the mineral oil that is sold specifically to care for wood chopping blocks.
It's the same stuff, but more readily available, and $2/16 oz. bottle, rather than $8.95/8 oz.
(If the bottle comes with too descriptive a label, discretion might warrant decanting or a homemade label announcing "for the cutting board" - to avoid embarrassing situations with guests in the kitchen.)