‘Hic’ inquis ‘veto quisquam faxit oletum.’
Pinge duos anguis ‘pueri, sacer est locus, extra
meiite.’ Discedo. — Persius, Sat. 1.112-114.
You say, “I forbid anyone to take a shit here!”
Paint two snakes. “Boys, this is a sacred place,
piss outside.” I depart.
In Persius’ Satires, the hallowed land upon which a tomb was built is used as a metaphor for the bounds of poetry. Essentially, the Julio-Claudian era satirist was noting that satire can be used irreverently to urinate upon the genre of epic. Persius’ words tell us something about the author and how he viewed his craft, but they surely also provide a window into the etiquette and apprehensions that surrounded Roman cemeteries. Oftentimes, it was inscriptions that articulated such anxieties, used as signs that stood guard like worrisome, Type A proxies for the deceased. Inscriptions could yell the dimensions of the burial plot or attempt to forbid an individual from reselling a tomb. Occasionally, they cursed those that might desecrate the tomb, and even pointed out certain behaviors–such as defecating or urinating–that were verboten.

I will get to some of these signs in just a second, but first I want to note that urination and urine were themselves ubiquitous in the cities of Roman antiquity. The “luxury latrines” (Magness 2011: 131) that sat dozens of patrons and which used running water from bathhouses, were few and far between in comparison to the use of the chamber pot. Such chamber pots were then regularly emptied into the street and (hopefully) carried away by overflowing fountains. Regardless of plumbing and the use of running water, I would go so far as to state that any man or woman who wished not to encounter urine would likely have to spend most of their time in a picturesque Virgilian forest rather than the streets of Rome. Persius was correct. Epic poetry rarely gives us insight into bodily functions.
Urine was itself only defiling in certain spatial and situational contexts, after all. The tanners and fullers who used urine were not religiously unclean for using urine in their occupations, but in Jewish communities, one could not recite the Shema while defecating or urinating on the toilet (cf. Deut. 23:15). Furthermore, it was not illegal to piss on the streets, it seems, but one was not allowed to piss on the statues of the emperor. Rumor had it that multiple men were put to death during the reign of Caracalla for urinating in areas occupied by busts or statues of the Severan (HA, Caracalla, 5).
Public urination could not be eradicated completely, but many attempted to relegate it to certain profane spaces via laws and signage. An inscription from Africa Proconsularis notes that Mars would be angry with someone if they were to urinate there (‘Si qui hic urinam / fecerit // habebit Martem / iratum‘ [AE 1949, 48]). The inscription appears to come from the pier of an arch in Thigibba Bure.
Still others turned to a little humor rather than to divine threats. Rather than simply cursing at passersby who might use their tomb as a latrine, an interesting epitaph from outside Rome asks the visitor to mix a drink and have one with the deceased. Kind of a Roman variation of pouring one out for one’s homies.

…Hospes, ad hunc tumulum/ ne meias ossa precantur/
tecta hominis, set si gratus/ homo es, misce bibe da mi.
Visitor, the buried bones of (this) man, beseech that you not urinate at this tomb, but if you are an agreeable man, mix (a libation), drink it, and give me some.
Another piece of evidence, a famous graffito from Pompeii, mocks the epigraphic beseeching of the visitor to respect the tomb.

Hospes adhuc tumuli n<e=I> meias ossa prec[antur]
nam si vis (h)uic gratior esse caca
Urticae monumenta vides discede cacator
non est hic tutum culu(m) aperire tibi
Visitor, these bones beseech that you not urinate at my tomb
for if you wish to be more pleasing to this (deceased man): shit!
You see the memorial of Urtica: get out of here, shitter!
It is not prudent for you to open (your) buttock cheeks here.
According to Kristina Milnor (2014: 65-66), the humor of the Latin scribble lies in the name Urtica (a stinging nettle [*ouch*]), which would have impaled the butts of anyone not following the graffito’s directive. If I had to venture a guess, I would say that the graffito is also mocking the rather serious language of signage implemented so as to control the behavior of the unruly men (and perhaps a few women) who wished to use monuments, tombs, and whatever other landmark that lay around as a toilet. Clearly the existence of law or social mores do not always equal social reality. In a clean world of epic (or perhaps Disney movies–I mean does anyone ever use a toilet in one of those?), we get the sweet-smelling ideal, but in satire and in epigraphy, we often get the obscenities of life.