As I went to mail at the mail box today, I noticed a spot where a large dog fertilized our front yard.

The owner of most of this subdivision is living temporarily in one of the homes a few doors up from us until his home in the country is completed.  He has two dogs, one small and the other large.  He doesn't have a fenced yard so he lets them run loose in the neighborhood and you know what happens.  They come in our and our neighbor's yards to water and fertilize our front yards.  It annoyed me so I called him and politely complained.  I'm trying to settle the matter with a Christian attitude by politely requesting that he not allow them to come in our yard and leave a mess because it really irritates me.

He explained that he understood my situation but that his problem is that he doesn't have a fenced yard. The city ordinance states that all dogs are to be on a leash, but I guess he thinks that law doesn't apply to him.

How would you handle the matter?

You politely asked that he handle the problem. He knows he is violating an ordinance. Give him a week or so to come up with a solution, if not call the local humane society (or whoever handles stray animals) to report that there is a large dog roaming the neighborhood. Give them a description of the dog and ask if they might suggest a way to handle this problem. Chat with the neighbors and tell them about how helpful the humane society was, oh and by the way here is their number in case you have a similar problem. I suspect that a few fines will "inspire" the gentleman to find a solution and multiple complaints from several neighbors will make it less likely that you will be targeted for any retaliation.

"Let every soul be subject to the governing authorities. For there is no authority except from God, and the authorities that exist are appointed by God.  Therefore whoever resists the authority resists the ordinance of God, and those who resist will bring judgment on themselves. For rulers are not a terror to good works, but to evil. Do you want to be unafraid of the authority? Do what is good, and you will have praise from the same. For he is God's minister to you for good. But if you do evil, be afraid; for he does not bear the sword in vain; for he is God's minister, an avenger to execute wrath on him who practices evil. Therefore you must be subject, not only because of wrath but also for conscience' sake. For because of this you also pay taxes, for they are God's ministers attending continually to this very thing" (Romans 13:1-6).

See also:

Questions and Answers regarding Neighbors