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Tony, I did a google search of "how good does Smelleze work" (something you could also have done), and it seems that Smelleze is for INDOOR odors such as mothballs, cat urine, and etc.
so NO,.... I don't think "Smelleze" will work on an 120'x80' cow pen with a 6 year accumulation of manure, but I have NO personal experience with the product so I can't say for sure.
Yes this is still the USA,... but,... as one "vet" to another, that doesn't give us a ticket to do what we want at the expense of others.
I'm sure you already know this, and I hope that is NOT what you meant by your comment.
As for a guess regarding your predicament, I'm guessing you have very little acreage, no pasture at all, and have more cows then you can eat in a year,... so the manure is building up and the smell is bothering a close neighbor.
If I were you,... I'd probably cut back on raising the number of "beeves" my family could eat each year (2), and even turn a small portion of my alfalfa field into a garden (but that is just what I would do, based on the details you've given us so far).
Someone else here probably has an even better idea than what I've posted.
I wish you well, and hope you get this figured out to your, AND your neighbor's, satisfaction.