I've read many posts where people complain about London broil or worry about it being tough. Most of what I've learned about smoking has come from this site, and it has changed my understanding of BBQ. I thought I'd share how I have been doing London broil for years. I'm sure people will weigh in with opinions this way and that and I look forward to reading them. I used to buy some of the steak marinades from the supermarket, and I noticed most just called for oil and vinegar plus the seasoning packet, so I thought well why am I paying for this crap, especially when they were not on sale and cost me 2 dollars each. I started with a simple oil and vinegar mix and some spog. over the years I've tried all different kinds of spice mixes, just about anything works. Montreal steak, adobo, lipton soup mix, but I always return to good old spogp what can i say I add a touch of paprika to my mix. Well anyway here is my process. Step one I use my meat tenderizer which I got from Costco and I can't recommend one of these enough. I prefer to buy choice, to me it's worth the extra money. You can see all the little holes it makes while also softening the meat and connective tissues. I can not stress this enough, I really beat the hell out of the meat with this thing. I find punching the meat with a good amount of force and very quickly works the best where the needles don't get stuck. Here is my simple marinade for today 1/2 cup apple vinegar 1/2 cup evoo some garlic powder, onion powder, paprika, black pepper, and pink salt. The great part here is just throw in whatever you like. I use very little salt because right before I throw it on the grill I will dump the marinade off and give it a fresh sprinkle of salt and pepper for that nice crusty taste. Remember to adjust the oil/ vinegar ration based on taste. I have found thin marinades penetrate the most and give more flavor throughout the meat. You can use anything from BBQ sauce to salad dressings. I dumped the entire marinade dish into a 1 gallon Ziploc with the London broil. I will let this sit in the fridge for at least a day, sometimes 3-4 days before grilling. I turn the meat over for even marinading every 12-24 hours. I will update this post when I remove the London broil from the fridge.