Actually, there is. Quite a number of ways, actually.
Theoretical: we understand a fair amount about radioactive decay and can *predict* on first principles the decay rates of most nuclei. We can then verify those rates in a lab. Unless you can give a reason why the fundamental principles would be different *and how* they would be different, this is good evidence that the rates are constant.
Observational: different methods, based on very different properties of the nuclei involved with wildly different decay rates, manage to give the same ages. This happens across numerous conditions and with a variety of different nuclei. Unless you can explain why conditions should have changed and explain how they could change in a way that makes things consistent across the different methods, across different produced ages, and across different conditions, the *evidence* is that they are consistent and give reliable results.
But it isn't simply radioactive decay involved in dating. We can also count, for example, varves in lakes or layers in ice fields. And, once again, the results obtained by simple counting agree with those obtained by radioactive decay AND the known events whose results are recorded (such as the eruption of known volcanoes at known dates). This is sufficient to show the Earth is *at least* hundreds of thousands of years old because we have counted ice layers agreeing with other methods going back past that.
The upshot: unless you can explain why hugely different methods, based on wildly different physical processes and in various situations across numerous obtained ages should be *consistent*, any denial is simply 'denying the evidence'.
Using the Omphalos argument without justifying it is simply denying the evidence.