There are some good tracks behind Forrest and Barwon Downs, but if it's been raining you won't get through.Lots of yellow clay
Heaps of fun but you would need mud tyres to traverse these tracks.Thompsons track behind Forrest is relatively easy and takes you through some nice parts of the Otway ranges.Goat track and Cowley track are also good.Just don't try Cowley drop off.I think it's been closed for a few years now anyway.You are guaranteed to end up on your roof or side on that track.Forrest is about an hour away from Geelong.Heaps of tracks around the area.Check out Stephensons falls also.There is a good hill climb out the back and the track will eventually bring you out in Gellibrand.
But if this is a bit far for you, you can't beat Angahook state forest.I've seen your piccies from before and I see that you have discovered some of the powerlines tracks.Lots of good, not-so-challenging tracks through the area.Just beware of swamp areas.I have seen a few other 4by's come to greif in them.Practically bottomless.Will fill up your rear brake drums straight away.Try Alardice track.But don't go down Cecil track.You will need bigger tyres, good suspension lift/flexability and a snorkel if the creek is full.
Hope you have fun