To guarantee you get the odds you want you need bet with a bookie so you secure the odds at the time.

If betting with TAB then you need to bet at the last possible moment (bet on Internet rather than by phone) and have access to a live update of the odds (Sky Racing is pretty good as long as your horse is in the top 8 - I do not have Teletext access but I believe the odds there are also fairly regularly updated). The odds shown on the various Internet sites are always a bit behind the Sky update. In my experience the NSW/QLD are better than than Tabcorp. Generally speaking if the TAB releases an update it appears on Sky within a few seconds and about 5-10 seconds later on NSW/Qld web sites - Tabcorp can take 15-25 seconds to update their web site.

If you want to bet into Tabcorp pool I recommend you have a look at the WA TAB site (ozbet.com.au) - the big advantage being you have up to a minute after your bet to cancel it (if race hasn't jumped). This can be good if there is a race delay (eg. horse breaks through barrier) and you want to review your bet or if they update the odds just before the jump and your horse has plunged it below your threshold.