Where to advertise for short term, pet friendly accommodation?

house sitting…

The only other idea is to look for people who are after house sitters because they are going overseas. Not sure where you’d look for that and whether pets would be an issue.
Landlords may be more open to pets now that the occupancy rate is getting lower.

You might just have to apply for places. Placing an ad doesn’t seem practical as there aren’t a lot of Landlords out there who trawl through the wanted ads and then phone people up asking if they want to come rent their house. You need to find someone specifically looking for a short lease, or a Landlord that’s willing to “settle” for you as a tenant.

hire a sky writer?

you could try c/t but i suspect its readership has dwindled (only those getting the hard copy are likely to flick to the classifieds) and likely expensive, but you could call them to discuss.

i’d have another go at gumtree and abide by their structure but put your details in the main text – users are probably savvy enough to see through the restrictions. good luck!