In the eternal domination game played on graphs, an attacker attacks a vertex at each turn and a team of guards must move a guard to the attacked vertex to defend it. The guards may only move to adjacent vertices on their turn. The goal is to determine the eternal domination number $\gamma^{\infty}_{all}$ of a graph which is the minimum number of guards required to defend against an infinite sequence of attacks.This paper continues the study of the eternal domination game on strong grids $P_n\boxtimes P_m$. Cartesian grids $P_n \square P_m$ have been vastly studied with tight bounds existing for small grids such as $k\times n$ grids for $k\in \{2,3,4,5\}$. It was recently proven that $\gamma^{\infty}_{all}(P_n \square P_m)=\gamma(P_n \square P_m)+O(n+m)$ where $\gamma(P_n \square P_m)$ is the domination number of $P_n \square P_m$ which lower bounds the eternal domination number [Lamprou et al., CIAC 2017]. We prove that, for all $n,m\in \mathbb{N^*}$ such that $m\geq n$, $\lfloor\frac{n}{3}\rfloor \lfloor\frac{m}{3}\rfloor+\Omega(n+m)=\gamma_{all}^{\infty} (P_{n}\boxtimes P_{m})=\lceil\frac{n}{3}\rceil \lceil\frac{m}{3}\rceil + O(m\sqrt{n})$ (note that $\lceil\frac{n}{3}\rceil \lceil\frac{m}{3}\rceil$ is the domination number of $P_n\boxtimes P_m$). Our technique may be applied to other ``grid-like" graphs.