I agree that the plan was solid.
Honestly, that truck falling so that the walkers could exit in humongous amounts pretty much gave them no choice. I thought it was fine plan, giving what they had to work with. According to Andrew Lincoln, they were dealing with over 40,000 walkers... any plan they came up with would of involved risk and people were to likely die regardless. They were on borrowed time.
Fire?
Great idea. Lets just add the risk of flaming walkers getting out to a forested area.
Bombing?
The military tried that and it worked out so very well.
Killing them in small quantities?
It's a herd of tens of thousands of walkers and more were filling up the quarry all the time. They could of potentially fortified the barriers and did it from a point of safety or tried to create a bottleneck to let a few out at a time but that would take a very long time, something they didn't have much of. Not to mention the amount of resources that would take.The number of walkers was massively increasing, Rick was right about any barrier they put up would eventually fail.
Rick's plan of leading the walkers away definitely had its flaws, but it was also working. The horn blowing - which is probably due to the wolves attacking - was unforeseen and shot that plan to hell, but unforeseen events could shoot any other plan to hell as well.
Anything they tried was going to run the risk of that herd getting to ASZ. There was an advantage to this plan though... once they had emptied the quarry out and lured the walkers 20 miles away - and the walkers would have kept going on their own further as we saw in season 2 - they could have then reinforced barriers to continue using the quarry to trap walkers in a more controlled, manageable way. Now that they know about it, they could send scouts out to check on it frequently and kill the smaller number of walkers that got trapped in there with less risk involved. Even with the horn blowing causing the plan to fail, they can still do that later.