"The Magen Avraham writes: 'It appears to me that it is forbidden to urinate on clay on Shabbos because of the prohibition against kneading.' The Magen Avraham means that it is even prohibited according to the majority of Poskim who are of the opinion that in the case of article which is kneadable into a proper dough-like mixture, one is not culpable for the Shabbos labour of Lash until he actually nkneads the mixture, since even according to these Poskimn there is nevertheless a Rabbinical prohibition involved even if one merely adds liquid to such an article. The same ruling applies to urinating on loose eart or sand."
(Mishnah Beruruah, 321:14:(57)) (Feldheim translation)
As I was learning this today a thought occured to me. Does God really care where I go to the bathroom on Shabbos?
It's a serious question. Here above me is the Master of the Universe, the Creator of us all. It is His essence that gives existence to me and everything around me. He has to worry about the lives of billions of people, animals, insects, plants, the atmosphere and everything else. Does He really care where I relieve myself on Shabbos? Is He sitting up there in Heaven with a little book and waiting for me to micturate on some loose dirt somewhere while on my Shabbos walk so He can say "Hah! Another strike against that nebbish!"
And after all I've learned, I have to conclude that He isn't and He doesn't care where I empty my bladder on Shabbos (well, if i do it in shul or on the dining room table that might be another story...).
So then why do I care about this halacha? Why am I learning Mishnah Berurah every day to get an understanding of what my obligations are in so many different situations?
The answer for me comes from Antignos of Socho in Avos 1:2: "Don't be like servants serving their master on condition of receiving a reward. Rather, be like servants serving their master not on condition of receiving a reward and let the fear of Heaven be upon you."
It's a well known story that Antignos' two disciples, Tzadok and Baytus, misunderstood their master and decided that their was no reward in serving God. The Tzadokim (Sadducees) and Baytusim emerged from them. But they didn't really get what Antignos was trying to say.
Consider what the role of an ideal human father is supposed to be. A father is to love and support his child, nurture him, give of his life energies to help that child succeed. His success as a father is measured by how well his efforts turn out.
And what does the grateful child do? He returns that love and commitment with as much of his being as he can. He strives to win his father's approval for there is nothing in the world more important to have than that. He struggles to succeed not because his father will hand him a cash payout at the end of the day but because his success as a child is measured by how his father responds to his efforts.
God is our Father in Heaven. How much more so does He give to us each and every second of our lives? How much grace has He shown us in all the miracles that have occured to our people throughout the ages and especially the last 60 years? And all He asks of us as His children is to strive to be the best we can in His service.
And therefore we as His children must struggle and strive to excel in every way we can so that we can win our Father's approval. Not because we expect riches, a nice house in Tahiti or a great job with a corner office (however, I'm not turning any of those down should they happen my way). We do it because, knowing what God has given us, we feel an obligation through our love for Him to return that through our actions.
So no, God doesn't care where I pee. I care because if I can take a simple bodily function and, on one day a week, exercise a little more care because I want to show that I care about the gift of Shabbos that He has given me and don't want to treat it like another day of the week, then I will.
Too much of Judaism in the last several decades has become negative. There are 365 negative mitzvos and 248 positive ones but when you read about the latest chumrah-of-the-week or the latest public "Daas Torah" you get the impression there is nothing but 1 negative commandment out there: Thou shalt not!" Is it any wonder more and more Jews are being turned off by their religion? That more and more are striking out because they're tired of being told "No" all the time no matter what it is to do?
You can say things in a positive way and in a negative way. "Don't urinate on the sand because it's Shabbos!" Why? "Because it's Lash!" Right, like anyone's ever kneaded a dough with urine and sand. What part of that doesn't sound stupid?
Instead, say "Keep Shabbos holy and make an extra effort. You gotta go? There's a piece of hard ground over there. Use it without any extra effort and know you did something positive." how much more reinforcing could that be?
We must always remember: God gave us his Torah so that we could happily proclaim His Word to the nations of the world. That Word is not "No, no, no!" It is that one can live a fulfilling, positive life within the boundaries of halacha without compromise. All you have to do is see the good things and strive for them instead of running from the negative.