The Dockers finished seventh and will play the sixth-placed Cats at the MCG, Sandilands saying Fremantle have respect for Geelong but do not fear them.
"They've won three flags in the last few years and they're probably the in-form side in the comp at the moment," he said.
"They're the reigning premiers, they had a great win over Sydney on the weekend, so they're in really good form.
"We know we've got to be on top of our game to beat them."
Fremantle have won eight of their past nine matches to storm into the finals but Geelong are still recognised as the team many would like to avoid in September.
Sandilands, though, said the Dockers would take confidence from their own recent form.
"I think our form over the second half of the year has been building really strongly," he said.
"Guys have got a great understanding of the game plan and we've just got to go out on the weekend and implement that."
The ruckman singled out the work of his midfield colleagues in the turnaround, particularly Michael Barlow, David Mundy and Ryan Crowley."Those guys have been in great form the second half of the year and done a really good job for us. They're just playing consistent footy," Sandilands said.
"Centre clearances are crucial and those guys are doing the job in there to get the ball inside 50 and lock it in there.
"(Crowley has) been really consistent this year in the role he gets. He probably gets the player in the side for the opposition each week and he's got to have a strong mind to come up against those opponents each week."
Nathan Vardy played his first game for season last week against Sydney, and the Cats are primed to select the rising star for Saturday night's clash along with first-choice ruck Trent West.
The Dockers played two ruckman in last weekend's win over Melbourne with Sandilands and Jon Griffin joining forces.
And Sandilands hinted they would probably go with the two talls again.
"If we're both in the same side together we've definitely got to be able to play up forward and both of us have an impact up there," he said."It was good that we both did kick a couple on the weekend and play a role for the side."