Regardless of what you do eventually your wood cutting board smells like garlic and onions. What do you use to clean it? I have several different methods but I wonder if someone has a better one.
Usually, I give it a good scrub with a damp sponge to get it a bit clean. And then I cut a lemon in half and rub the entire board down with the cut side of the lemon. Sometimes, I'll do that a few times (rub it down, let it dry, repeat).
If things are very bad, I'll use fine grain sand paper to take a thin top layer off, oil it down again, and leave the oil to set for a day or two without using.
First a bath in soapy water then we occasionally pour boiling water over them too
Ditto what nomivorous said, except that I add a good teaspoon of seal salt or kosher salt to the lemon half when I scrub the board down. Salt is a natural anti-bacterial agent, and the combo of lemon juice and salt, not only cleans, but naturally sanitizes the board. Give it a thorough rinse with hot water, and it's good to go. Depending on how much use your board gets, I rub my board with a good, neutral vegetable oil when the spot that gets the most use becomes dry and pale compared to the rest of the board. (about once a month in my case). And yes, I try to pick a time (like leftovers night, or before a weekend away) to oil the board so it has a chance to rest for a day or two.
I scrub mine with some coarse salt and a half a lemon and sand it down every now and then so stuff doesn't get stucks in knife cuts ....
Odors are particulate. That means if you smell onions on your cutting board, there are, indeed, onions on your cutting board. I use a (very) diluted bleach solution. It takes care of the germs and the odor in one fell swoop.
A good safe bleach solution is 1/2 teaspoon to 1 quart warm (about 100 degrees) water. I have to confess that for smelly stuff I use plastic boards that I can put through the dishwasher.
Yes, I should also stress that I ONLY use my wooden cutting boards for vegetables, nuts, fruit, and cheese. Raw or cooked meat, fish and poultry go on clean, plastic boards that can be popped in the dishwasher and sanitized at high heat.
I had the same problem recently. I used a combination of answers from my pickle reponses. This what worked best for me. Many lemons + copious amounts of baking soda + kosher salt. Cut lemons in half and squeeze them on to the board making a paste with the salt and baking soda using the lemon halves as a scouring device, let it sit for about 10 minutes, rinse, repeat as necessary.