A daily chore gives flea dates a daily audience
Flea treatments repeat often enough that a reminder seen daily beats a clever system checked rarely. The wall calendar by the litter station is in front of you during scooping every single day, which means treatment circles drawn on it are reviewed dozens of times per cycle without anyone deciding to check anything. That passive repetition is ideal for catching the slow drift that defeats flea control: a treatment done a few days late each time until the gap is wide enough for fleas to gain ground. Hang the calendar so the current month sits at eye level while you work, with a marker on a string so marking takes seconds.
Circles that distinguish due from done
The marking convention carries the whole system, so keep it strict. In advance, draw a circle in the cat's colour on each due date, with her initial inside. The treatment is recorded only when the circle is crossed through with a firm line on the day it is applied. An uncrossed circle is therefore an honest, visible debt, and anyone scooping can read the month at a glance: crossed circles are handled cats, open circles are outstanding work. If a treatment happens late, cross the circle on the original date but write the actual date beside it, preserving the truth about the gap instead of tidying history.
One colour per cat prevents the reassuring mistake
In a multi-cat home the wall calendar's characteristic error is false reassurance: seeing marks on the page and assuming every cat is covered, when the marks all belong to the easy cat who presents herself, and the shy cat's dates passed unmarked. A fixed colour per cat, written in a small key at the top of the calendar, makes an untreated cat visible as the colour with open circles. When a treatment is applied by someone else, a partner, a sitter, a teenager, the rule is that they cross the circle in that cat's colour themselves, because a verbal assurance that evaporates by evening is how double and missed treatments both happen.
The pre-month-end sweep while you scoop
Build one active check into the passive system: during the last few days of each month, while scooping, read the whole page deliberately rather than in passing. Any open circle gets resolved before the page turns, either the treatment is done and crossed, or the reason it is being held, veterinary advice, a skin reaction still settling, is written beside it so next month's page inherits the explanation. Copy next month's due circles onto the new page during that same sweep, in the same colours, before the old page comes down. That ten-minute ritual is what makes a paper calendar behave like a system instead of a decoration.
Pages get torn away; the history should stay
A wall calendar's record is deliberately disposable, which is fine for prompting and poor for proof. When a vet asks how consistently a cat has been covered, whether a reaction followed a particular application, or when a boarding stay requires evidence of current protection, last season's torn-off pages cannot answer. Keep a lasting copy of the dates as you go, even a photographed page each month beats nothing, and attach the sequence to the cat's own records. KinsLe Pet Passport gives the dates a permanent address in this cat's own record, so a question at the surgery gets answered from her history rather than from a page already in the recycling.