Ever heard of homeopathic piss?
A forensic scientist could probably trace urine in a shower cubicle. They would almost certainly trace a whole bunch of other nasty stuff too – so you’re probably best off just not having a shower.
You physically contact a hundreds of other really gross things in your daily life, they are avoidable unless you’re a regular Howard Hughes. Minute traces of your partners urine on the soles of your feet really are the least of your worries.
Let it flow folks