Never been to Trusty's Fort, no. Inverurie is pretty-much the epicentre of ancient Aberdeenshire, so you have a huge choice of sites that way! I'd also suggest you consider having a look at the Maiden Stone - A very fine Pictish carved stone just up the hill off the A96 at Pitcaple - and if there, if you walk down the hill a little bit, on the right is "Persephone" - a large modern sculpture in a little glade just off the road (no parking though).
Also nearby is Insch and the Picardy Stone - another very fine Pictish stone, plus the short walk to the hillfort at Dunnideer - which has superb views, several phases of occupation/construction into medieval times and hut circles cut into the hillside. There are a couple more ancient sites/circle remains in the same area but all significantly damaged or in fields that usually have livestock.
Information about and images of the Picardy Stone Pictish stone in Aberdeenshire on Undiscovered Scotland.
www.undiscoveredscotland.co.uk
Vitrified Fort in Aberdeenshire, Scotland
www.megalithic.co.uk
That little cottage just along the road from the Picardy Stone to Dunnideer was where my family got its Aberdeenshire roots down after coming from Moray via Buchan - it is restored as a private house now after a long time in ruins.
Also, over the hill is the large ruin of the mansion of Wardhouse, once home to Admiral Sir James Alexander Gordon, who was the inspiration for CS Forester's Horatio Hornblower! I have driven-up and had a look - the old steading/square beside it is still occupied but the house itself is visitable. Unless someone has started restoring it - there was talk of that maybe happening a couple of years back but it could be all hot air.
Also easily reached from Inverurie via the lovely "Lords Throat" back road along the river Don and the back O'Bennachie is the Old Keig stone circle. The biggest recumbent of them all and in a great location. There is a large place for forestry/farming trucks to park just at the head of the strip of trees it sits in, just jump the fence and walk down. The Modern Antiquarian site talks about people feeling "unwelcome" but I've never been bothered on any visit over many years and the last time I was there, I was pretty certain the nearby farm is no longer occupied or sold-off as a private house.
Old Keig
You could make a nice circular to Kemnay that way.