i've covered up marks on wood flooring with felt tip pens before....:?
waxing sounds like a good idea though - also, he's consented to you having a dog in the property. i'd imagine this leaves him with little room to complain about the scratches on the floor (unless he's prepared to provide you with some booties for the dog to wear inside)
i assume a good inventory was taken before your tenancy began?
marks on the wall? sugar soap and a good roller for the paint will sort it out (no paint brush streaks).
as for picky landlords, the last place i rented (years ago) had us come back to wipe off marks on the light switches (basically a small amount of fingerprints left on them as they were brass switches!) had to leave the property and turn them off with my bike gloves on! f**king pedant!
you seem like a genuine chap, with the best intentions.
if you leave the place in good condition (or as close to as it was when you moved in) the landlord has little ground to stand on.
some landlords take the piss, some tenants take the piss. luck of the draw really for both sides.
our tenant had a sky dish installed. i hate it, but i hate it more that we were not notified of it - it involves work done to the property that could lead to damage - and to add to that, we have a share of freehold, so would imagine any exterior work/alterations would need to be consulted with freeholder as well. (given the shoddyness of some installations i've seen in the past), so its a good idea to get the landlords 'permission'. not sure on the legals of them being able to 'deny' it though. but thats another discussion i guess.
good luck with the visit!