I have put my tripod inside the checked-in luggage. No problems or whatsoever, unless you feel it is too heavy and may increase your luggauge weight. When my tripod is inside, I did not have any problem passing thru the Australian Custom. At Sydney Airport, I went to the "Things To Declare" gate and let the scanners do the job. I went there as I declared having some Chinese medicine and shoes. Read the card and you will know how strict their custom is.
If unsure, just tick you have things to declare when you are filling up the Australia Arrival Form. Lastly, "Declare or Beware"