Animal on lead comes across perfect place for a tinkle (5,3)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

So not lamppost/leg lifting, then. The animal is an OX, placed at the back of PB, lead, enclosing (across) HONE for perfect (accent on second syllable). Phone boxes, an increasingly rare sight, are renowned for both sorts of tinkle.